Category Archives: Science and Society

“Fair-weather” scepticism

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My old man used to label us kids as “fair-weather sailors” when we bitched about working outside during bad weather.

That phrase comes to my mind sometimes when I come across people who claim to be “sceptics ” (“Skeptics”) behaving very unsceptically when confronted with a claim outside their area of interest. For example, someone who can be quite objective about scientific claims but reacts quite unobjectively to political claims.

Perhaps politics is a bit like religion to some people – they line up instinctively on one side or another. However, I think a true sceptic should still be able to consider political claims according to the facts available and not just rely on instincts.

So, I am all for this image. Yes it is hard. But when you think about it what use are one’s ingrained prejudices if they do not stand up to sceptical consideration.

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Poor peer-review – a case study

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“Peer-review” status is often used to endorse scientific papers cherry-picked because they support a bias.

Many scientists are not impressed with the peer-review processes scientific journals use. Like democracy, this peer-review is better than all the available alternatives but it certainly doesn’t guarantee published scientific papers are problem-free.

Sure, peer-reviewed sources are better than others which have no quality control. But it is still a matter of “customer beware.” The intelligent users of scientific literature must do their own filtering – make their own critical judgements of the likely reliability of reported scientific findings.

Despite this people often use the “peer-reviewed” description to endorse published finding (especially if they confirm their own biases) without any critical assessment. This happens a lot in on-line debates of “controversial” issues.

Here I will go through the details of peer-review of a recently published paper which anti-fluoride activists are endorsing and promoting, but others are critcising. The paper is:

Malin, A. J., & Till, C. (2015). Exposure to fluoridated water and attention deficit hyperactivity disorder prevalence among children and adolescents in the United States: an ecological association. Environmental Health, 14.

I have discussed this paper in recent posts (see More poor-quality research promoted by anti-fluoride activists and ADHD linked to elevation not fluoridation). The journal, Environmental Health, has a transparent peer-review process which provides access to the names and reports of the reviewers. This reveals problems with the review process in this case. Below I discuss the responsibility of the authors, reviewers and the journal for the problems with this paper and its reported findings.

Authors’ responsibilities

The authors are clearly committed to a pet theory that fluoride is a neurotoxicant which could contribute to ADHD prevalence. Nothing wrong with that – we all feel committed to our hypotheses. We wouldn’t be human if we didn’t. But the best way to produce evidence for a hypothesis is to test it in a way that could prove it wrong.

In this case the authors found a correlation between ADHD prevalence in US states and the amount of community water fluoridation in each state. Trouble is, one can find just as good a correlation, or even a better correlation, with many other criteria for which state prevalence statistics are available. I listed a few in  ADHD linked to elevation not fluoridation. Some of these factors are also correlated with community water fluoridation suggesting the correlation reported by Malin and Till (2015) may be deceptive.

A proper test of the fluoridation hypothesis would include considering the effect of including such confounders together with fluoridation in their statistical analysis. Malin and Till (2015) did include one other criteria – the median household income for 1992 – but did not include any others. I find this surprising because they acknowledged ADHD results from interaction of genetic and environmental factors. While fluoridation is not usually considered a relevant factor things like smoking and premature births are and there is conflicting evidence about the role of economic factors like poverty and income.

In my article  ADHD linked to elevation not fluoridation I showed ADHD prevalence is better explained by a few of these factors without any input from water fluoridation.

I can’t help feeling the limited consideration of confounding factors results from a desire to protect the fluoridation hypothesis and therefore not test it properly.

Reviewers responsibilities

Again, such a desire is only human. But reviewers should have picked this up during their own considerations.

Interestingly, only one of the two reviewers raised possibility other confounders – specifically lead levels. This is of course valid as lead is a recognised neurotoxicant – but why did none of the reviewers question why other factors like smoking, premature births and social or regional factors were not considered?

I believe that is because both reviewers had research interests directed at chemical toxicity and not ADHD or similar mental characteristics. A matter of someone with a hammer only seeing nails.

The reviewers and their research interests are:
Marc Weisskopf whose reviews are available here and here.

“Some examples of my current work are exploring how exposure to, e.g., lead, manganese, and air pollution affect cognitive function and psychiatric symptoms; how exposure to Agent Orange and other herbicides used in Vietnam relate to the development of PD; and how formaldehyde and lead exposure relate to the development of ALS.”

Anna Choi whose review is here.

“Dr Choi’s research focuses on the effects of environmental exposures on health outcomes. She has been studying the birth cohorts in the Faroe Islands where exposures to environmental chemicals including mercury, PCBs, and PFCs are increased due to traditional marine diets. In addition, she also studies the effects of the contaminants on cardiovascular function and type 2 diabetes among the Faroese septuagenarians. She is also actively involved in the research on the impact of nutrients as possible negative confounders that may have caused an underestimation of methylmercury toxicity. Dr Choi’s other research interests include studying the adverse effects of fluoride exposure in children.”

Why were reviewers with a wider research experience not chosen? This journal allows authors to propose suitable reviewers themselves. Or the reviewers may have been chose by the associate editor handling this paper – Prof David Bellinger. His research focuses on the neurotoxicity of metabolic and chemical insults in children. So again it may just be the blinkered view of someone whose research background stressed the role of neurotoxicants rather than other factors likely to influence ADHD prevalence.

The journal’s responsibility

I noticed that one of the two chief editors (who have final say over acceptance of submitted papers) of this journal is Prof Philippe Grandjean. He himself has been actively promoting the idea that fluoride is a neurotoxicant purely on the evidence of the metareview of Choi et al (2012). Yes he is a coauthor of that review and Choi is one of the reviewers of the Malin and Till paper. The review of Choi et al (2012) related to areas of mainly China where fluoride concentrations are higher than used in community water fluoridation. Areas where endemic fluorosis is common.

I have to wonder if Grandjean’s well-known position on fluoride and community water fluoridation was a consideration in choosing this journal for publication.

Others have commented that the journal Environmental Health is considered low-quality based on its low impact factor. I do not know the area well enough to pass judgement myself. However, I notice that the journal charges authors for publishing their paper (£1290/$2020/€1645 for each article accepted for publication.) This sort of charge, associated with poor quality peer-review makes me suspicious. I have commented on these sort of journal before in my post Peer review, shonky journals and misrepresenting fluoride science.

Conclusions

This is one example of peer-review and paper acceptance which brings into question the idea of using  publication and peer-review as endorsement of a study’s   quality. I am sure this is not an isolated case. Even with the best of intentions journal editors and reviewers are limited by their own areas of expertise. Journal publication and peer-review is a far from perfect process – even if it is preferable to current alternatives.

Unfortunately activists will promote poor quality studies like this by blindly using the study’s peer-review status.

The intelligent reader should beware of such blind endorsements. Knowing the human foibles which exist in the research and publication processes such a reader will consider the contents of the paper and not rely on peer-review status. They will consider the evidence and conclusions critically. And if they don’t have enough background to make their own critical assessment they will consider the views of others with the required expertise and not blindly accepting what political activists tell them.

Footnote

Just came across this article referring to peer-review problems in journals published by BioMed Central – Major publisher retracts 43 scientific papers amid wider fake peer-review scandal.

BioMed Central publishes the Journal Environmental Health discussed in this post. I am not suggesting this paper was part of the peer-review racket discussed in the article. But the news item does highlight the point I am making that intelligent readers need to consider published scientific papers carefully and critically and not blindly rely on “peer-review” endorsement.

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The arrogance of science?

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This comment of Richard Feynman’s indicates to me the essential humility of science. Yet we often find that people who seem to subscribe to the support of “answers that can’t be questioned” will accuse science and scientists of arrogance.

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I suspect this is because they have put themselves in the position of being unable to support the claims they are making.

ADHD linked to elevation not fluoridation

Attention-Deficit Hyperactivity Disorder (ADHD) is more likely linked to residential altitude than community water fluoridation (CWF). This finding calls into question a recent paper claiming ADHD is linked to CWF. A paper that is being heavily promoted on social media at the moment by anti-fluoridation groups.

I discussed problems with that paper, (Malin & Till, 2015) in my article More poor-quality research promoted by anti-fluoride activists. Now I have taken my critique further by making my own exploratory investigation of likely influences on the prevalence of ADHD in US states using the approach of Malin & Till,(2015). Except I did not limit my investigation to CWF  data but also included state prevalence data for other likely influences on mental health.

ADHD linked to elevation

Elevation One of the best correlations with ADHD state prevalence I found was with elevation data for each state. It’s a negative correlation – the higher you go the lower the prevalence of ADHD This figure shows the correlation of ADHD state prevalence in 2011 with mean elevation for the 51 states. It is statistically significant with a correlation coefficient (r) of -0.5 and significance (p) of 0.00.

Fluoridation-2010For comparison, the similar correlation of ADHD state prevalence in 2011 with prevalence of CWF in 2010, while significant, has a correlation coefficient of +0.32 and significance of 0.02. However, the correlation with CWF is not significant in a multiple regression with elevation – see below.

Other factors worth considering

My exploratory statistical analysis showed a number of other factors significantly linked to ADHD with correlations similar to, or higher than, CWF. Images for the data and a table of correlation coefficients and their significance are shown below.

The correaltion of ADHD state prevalence in 2011 with home ownership and % living in poverty are better than with CWF. These correlations are positive – the prevalence increases with % home ownership and % of people living in poverty. I guess it is hardly surprising that mental health problems would increase with the amount of poverty. But perhaps in the US home ownership is also not conducive to mental health?

Home-Poverty

The correlations of ADHD state prevalence with educational attainment (Bachelors degree) 2009 and Per Capita personal income 2010 were similar to that with CWF. These correlations are negative – I guess its easy to understand that higher incomes and better education is conducive to better mental health (lower prevalence of ADHD).

Education-Income

over-65

The correlation of ADHD state prevalence with the proportion of the sate’s population older than 65 was also similar to that for CWF. The correlation is positive and one can only speculate on reasons for the increase of ADHD prevalence as the proportion of older people increases.

The table below summarises correlation coefficients (r) and statistical significance (p) for the figures above.

Correlation of ADHD state prevalence with a range of factors

State data Correlation coefficient (r) Statistical significance (p)
Mean elevation -0.50 0.009
CWF 2010 % +0.32 0.022
Home ownersip % +0.38 0.005
Poverty % +0.37 0.007
Education (% Bachelor’s degree) -0.35 0.011
Per capita income ($) -0.32 0.022
Age over 65 % +0.30 0.031

Multiple regressions

CWF in 2010 is correlated with mean elevation – correlation coefficient r=-0.43 and significance p=0.002 – suggesting these are not independent variables. (CWF in 1992 was similarly highly correlated with mean elevation.) Perhaps Malin and Till (2015) only found a correlation of ADHD with CWF because they are both related to mean elevation.

Multiple regression analysis suggests this is the case. The statisitically significant factors were mean elevation (p=0.001), home ownership (p=0.000) and poverty (p=0.005). The contribution of CWF in 2010 was not statistically significant in this multiple regression (p=0.587) as were most of the other factors I considered.

Malin and Till (2015) use the CWF for 1992 in most of their comparisons. My analysis shows this has a better correlation with ADHD prevalence in 2011 than CWF for any other year (r=0.45 cf 0.32 for CWF in 2010). It seems strange to use 20 year old data in  a model predicting ADHD prevalence for 2011 so I used more recent data for my exploratory analysis. However, in a multiple regression the contribution from CWF in 1992 was still not statistically significant (p= 0.158).

Conclusion

We should be careful of conclusions arising from such exploratory investigations. Firstly the obvious – correlation is not causation. But secondly the choice of data  is crucial.

Malin and Till (2015) chose to consider CWF prevalence as the main factor influencing ADHD prevalence. They did also include socioeconomic status (SES) as a secondary factor.  However, my analysis shows a number of other factors which could equally be considered. And when they are considered in multiple regressions the contribution from CWF is not statistically significant.

modelThe model used by Malin and Till (2015) using CWF in 1992 and SES in 1992 explained only 31% of the variance of ADHD prevalence in 2011. The corresponding firgures for ADHD prevalence in 2003 and 2007 were 24% and 22%.) But using a model for the influence of mean elevation, home ownership and poverty only (no CWF included) I was able to predict the state prevalence of ADHD in 2011 as shown in this figure. This accounts for 48% of the variance and has a significance of p= 0.000. Perhaps further exploration of the available data could produce an even better model but the key point here is that CWF does not contribute anything once mean elevation is included.

I do not think Malin and Till (2015) are justified in drawing the conclusion that CWF influences ADHD. Their mistaken conclusion has arisen from their limited choice of data considered for the exploratory analysis. That in itself seems to have resulted from a bias inherent in their hypothesis that “fluoride is a widespread neurotoxin.”

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Anonymous comments on social media

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Something I picked up on the internet.

Yes, I know – some people have legitimate and understandable reasons for being anonymous when they comment on social media. Concern for jobs and protection for family and self.

I can appreciate that and have no issue with those people.

But there is just such a lot of rubbish spouted by anonymous commenters on social media. I can only conclude the reason for anonymity of these hostile and drive-by commenters is that they are at least subconsciously aware of the rubbish they are promoting so do not want their name associated with it.

Whatever their reason, anonymity seems to bring out the worst in these people. and they waste a lot of time for others who attempt to debate them.

More poor-quality research promoted by anti-fluoride activists

Anti-fluoridation propagandists must think all their Christmases have come at once. They at last have a “peer-reviewed” scientific paper they can claim supports their position. What’s more, it is the second such paper to appear in the last month.

But they really are resorting to arguments of quantity (2 papers) over quality. This new paper claiming a link between community water fluoridation (CWF) and Attention-Deficit Hyperactivity Disorder (ADHD) is of just as poor quality as the earlier one claiming a link with hypothyroidism. Both papers are speculative, ignore other relevant factors, and “prove” nothing.

I discussed the hypothyroidism paper in the article Paper claiming water fluoridation linked to hypothyroidism slammed by experts. The new ADHD paper is:

Malin, A. J., & Till, C. (2015). Exposure to fluoridated water and attention deficit hyperactivity disorder prevalence among children and adolescents in the United States: an ecological association. Environmental Health, 14.

Here are my thoughts on this paper.

Exploratory investigation – correlation not causation

The authors have simply taken existing online data and searched for a statistically signficant relationship. They have explored the limited data sets used – not attempted to prove an effect. After all, correlation does not prove causation – the graph below shows an example of how correlation can often produce meaningless results.

The data sets Malin and Till (2015) used are both from the USA Centers fo disease Control (CDC).

  1. State-based attention-deficit hyperactivity disorder (ADHD) prevalence (Visser et al., 2014);
  2. Numbers of people receiving fluoridated water from public water supplies in each state obtained from the CDC.

Note, they did not use data for individual children exhibiting symptoms of ADHD  determined by  a health professional. The data was from random surveys “in which parents were contacted via telephone and asked about the emotional and physical well-being of a randomly selected child from their household.” Similarly they did not use data for dietary intake of fluoride by individual children but used “the percentage of the U.S. population on public water systems that receives optimally fluoridated drinking water.”

They have assumed these data are reliable proxies for occurrence of ADHD and fluoride dietary intake. But the data could represent other factors as well.

For example, parental reporting of ADHD could differ from state to state because of differences in parental educational levels and ideological attitudes. People in  different sates may not have the same level of knowledge, awareness or acceptance of such behaviours. Malin and Till themselves acknowledge ADHD reporting is higher for parents with a high school education than for parents who did not graduate high school (Visser (2014). Parental education levels are likely to vary from state to state.

The availability of CWF can be dependent on the size of urban areas for both technical reasons and because of  recognised willingness for innovation from large and high status city leaders (Crain, 1996) so that the state prevalence used could be acting as a proxy for the distribution of urban areas of different sizes, and the relative urban/rural distributions in different sates. A correlation may indicate nothing more than a relationship between city sizes and parental education.

The authors themselves warn their study has limitations, saying it is:

“an ecological design that broadly categorized fluoride exposure as exposed versus non-exposed rather than collecting information related to concentration of fluoride and patterns and frequency of exposure or outcome at the individual level. Future research could explore the relationship between exposure to fluoridated water and the occurrence of ADHD at the individual level.”

And, again, we should always keep in mind that correlation does not prove causation.

The starting hypothesis

Inevitably any serious exploratory investigation should start with a working hypothesis. As psychologists the authors are presumably interested in ADHD and its causes. But why investigate state prevalence of CWF instead of any of the other factors indicated in this condition. In fact they list a range of candidates from arsenic and lead to food additives and food colouring. Granted, they saw CWF as a field ripe for plucking as they say fluoride “has received virtually no attention in the ADHD literature.” But I would have expected them to at least include these other known factors as confounders in their study.

I think the answer lies with their biased reading of the literature. They start with the claim that fluoride is a “widespread environmental neurotoxin,”  but only really cite Grandjean and Landrigan (2014) and the closely-related meta-analysis of Choi et al., (2012) to support this claim. I have discussed those papers and their problems in  Repeating bad science on fluoride and Controversial IQ study hammered in The Lancet. A major problem with that work is it involved areas of endemic fluorosis where fluoride intake is high so it is not directly relevant to CW. In fact, the authors’ bias is indicated by the fact they did not cite Broadbent et al., (2014) which showed no neurotoxic effects of CWF. Broadbent et al.’s paper is directly relevant to CWF – Choi et al.’s is not. (I discussed the differences as indicated by dental fluorosis data in my article Water fluoridation and dental fluorosis – debunking some myths

I feel this omission indicates that the authors resort to the special pleading of anti-fluoride activists in the citations they used for justifying their starting hypothesis. The also rely on studies of rats fed very high levels of fluoride, such as that of  Mullenix et al., (1995), and then use her weak argument to claim relevance to CWF by comparing  rat blood plasma F levels to those for humans ingesting high levels of fluoride. (See my article Peer review of an anti-fluoride “peer review” for a discussion on this). Similarly, although acknowledging the high F intake levels of most of the studies reviewed by Choi et al., (2012), they excuse this by referring to the one study with low levels (0.88 mg/L) – ignoring the fact this was a one and a half page article in a newsletter describing measurements in an iodine deficient area. In this study (Lin, et al., 1991) children from low iodine areas were compared with a group from another area that had received iodine supplementation. About 15% of the children suffered mental retardation, 69% of these exhibited subclinical endemic cretinism. The effect of iodine supplementation was clear, the effect of fluoride not so clear. (See Peer review of an anti-fluoride “peer review” for further discussion of this).

So, I think the justification for their starting hypothesis is hardly objective

“Natural” vs “artificial” fluoride

Despite  problems with justification for their hypothesis they did find a significant positive relationship between the US state prevalence of parent-reported ADHD in children and the state proportion of water supplies with optimum levels of fluoride. Again, not a proof of their hypothesis, but interesting data to consider nonetheless. They found inclusion of socio-economic status data improved the relationship but did not consider other relevant confounding factors like parental education and exposure to relevant chemicals.

In contrast, the relationship they found between ADHD prevalence and natural fluoride prevalence (at optimum level or above) was negative and statistically signficant. This actually conflicts with their starting hypothesis of chemical neurotoxicity based on the work of Choi et al., (2014) and Grandjean and Landrigen (2014). While they concede the data really doesn’t allow a conclusion they suggest it could result from the ADHD effect being specific to “fluoridation chemicals” and not fluoride itself.

This leads them to suggest a theoretical “pathway” for CWF contributing to ADHD – the corrosion of lead-bearing plumbing by fluorosilicic acid. Trouble is this ignores the well established fact that fluorosilicates used in CWF decompose to form silica and the hydrated fluoride anion when diluted in water. Malin and Till seem oblivious to work showing this and rely instead on citation of the poor quality work of Masters and Coplan to support this “pathway.” Another example of their citation bias.

But their proposal does raise an important question. Given that lead is one suggested cause of ADHD why did they not concentrate their exploratory analysis of data for lead intake by children in different states, rather than CWF prevalence? Or at least include lead levels as confounders in their statistical analysis.

The thyroid story again

Their second suggested “pathway” is via suppression of thyroid gland activity by fluoride. But, again, this hypothesis does raise the question of other causes, in particular iodine deficiency. (See my discussion of Peckham’s paper – Paper claiming water fluoridation linked to hypothyroidism slammed by experts – for more on this). If this was part of their starting hypothesis then why not consider data for state prevalence of iodine deficient diets of children? Or or include this as a confounder in the analysis?

I find it interesting that despite declaring a starting hypothesis based on the chemical toxicity claims of Choi et al., (2012) and Grandjean and Landrigen (2014), Malin and Till have not proposed any theoretical “pathway” involving direct neurotoxicity of fluoride itself to explain their result. This makes their unwillingness to consider other relevant confounding factors even more obvious.

Conclusions

As I wrote above correlation is not causation  and this study does not “prove” anything. The observed “link”could represent a number of other relationships which are not directly associated with CWF. The analysis also suffers from a lack of consideration of obvious confounding factors.

I believe this is the sort of problem that arises when researchers have a committment to a starting hypothesis and peer review systems are inadequate. Such studies are a problems when published because ideologically motivated activists love to cherry-pick them to claim “scientific support” for their cause. This is not helped when the researchers themselves climb on the activist bandwagon and attempt to claim more for their findings that is really justified.

I think Malin and Till have done this with the press release from their department – Fluoride in tap water associated with ADHD in children, researchers find. It is one thing to say:

“Our findings showed that artificial fluoridation prevalence in 1992 predicted ADHD prevalence in 2003, 2007 and 2011 among children and adolescents in the United States, and that was after controlling for median household income.”

But the careful claim their “findings showed” a “prediction” is far too easily seen as proof in the mind of the lay-reader. Worse, they draw unwarranted conclusions from their limited work:

“As citizens of Toronto, living in an artificially fluoridated community, I think we need to ask ourselves whether this is still a worthwhile practice.”

One can only pose such questions in the context of an objective assessment of their own work together with other research of possible harmful and beneficial effects of CWF. I think their biased choice of citations in this paper shows they are not capable of doing this.

On the other hand reviews such as the recent NZ Fluoridation Review, Health effects of water fluoridation : A review of the scientific evidence, have done this. Community leaders should be going to such sources for their information and not rely on cherry-picked poor quality studies like Malin and Till (2015) which will be promoted to them by anti-fluoride propagandists and activists.

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Free download – “Severe dental fluorosis and cognitive deficits”

S08920362Anyone interested in my article on this subject in Neurotoxicology and Teratology can now download a pdf version:

Perrott, K. W. (2015). Severe dental fluorosis and cognitive deficits. Neurotoxicology and Teratology, 48, 78–79.

The publishers tell me that anyone who clicks on the link until May 3, 2015, will be taken to the final version of on ScienceDirect for free. No sign up or registration is needed – just click and read!

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Are submissions on fluoridation worth it?

Like most people I struggle to find the energy when representative and government bodies call for submissions. But I did make the effort recently when Medsafe called for submissions on their proposed clarification of how fluoridating agents are defined in the medicine regulations. I am pleased to see the simple suggestion I made was accepted. But my purpose here is to illustrate how this consultation proceeded and how opponents of community water fluoridation (CWF) tried to swamp it with their submissions.

The background

Last November the Ministry of Health (MoH), through Medsafe, called for submission on a change to the Medicine Regulations 1984. This change had been recommended by the High Court and the Crown Law Office who specifically suggested that fluoride compounds used for CWF be exempt from definition as a “medicine.” This arose from the defeat of attempts by an anti-fluoride group, New Health NZ, to use the argument that fluoridation was medication in the High Court actions against CWF. Despite these defeats the High Court and Crown Law Office considered the regulations should be clarified to remove the argument from repeated litigation.

Simply, the proposal was to add a new regulation:

“Fluoride-containing substances, including the substances hydrofluorosilicic acid (HFA) and sodium silico fluoride (SSF) are not medicines for the purposes of the Act when they are manufactured and supplied or distributed for the purpose of fluoridating community water supplies.”

Medsafe asked for responses to the following questions:

  • Question 1: Do you support the proposed amendment? If not why not?
  • Question 2: Are there other fluoride-containing compounds used to treat community water supplies that should be specifically named in the regulation? If so, what are they?

Submissions – quantity or quality

The report from MoH on the process and their recommendations to cabinet give an idea of the submissions made and the final decision.

As we might expect from past experience the submissions were dominated, in numbers if not quality and relevance, by those from the anti-fluoride groups. They had organised a national and international campaign to swamp Medsafe. Paul Connett’s Fluoride Action Network, Fluoride Free NZ and New Health NZ even provided texts and templates to copy and paste into submissions.

Here is the description of the consultation outcome in the MoH report:

MOH-report-extract

So, the activist organisations can certainly mobilise their forces for submissions. But concentration on numbers and not content – and cynical provision of content to followers anyway – didn’t win them any credence. Did they really think blatant duplication of submissions would not stick out like a sore thumb?

It is also heartening to see that the MoH was not swayed by blanket repetition of arguments which do not have credible scientific support. (I guess we can also see why the anti-fluoride activists groups are putting so much effort into their campaign to attack and discredit the NZ Fluoridation Review which summarises the scientific evidence.)

Sometimes suggestions are accepted

I had made the simple suggestion tha sodium fluoride be added to the short list of examples of fluoride chemicals used for CWF. So this recommendation to cabinet pleased me

recommend-to-cabinet

Nice to know that the consultation was not a sham and that reasonable and credible suggestions were listened to and even accepted. It is worth making submissions even when one is aware they me in a minority. If something is worth saying it should be said despite attempts by others to confuse issues.

Also nice to know that some consultations are not simply swayed by quantity and not quality – as was the case for the Hamilton City Council fluoride consultation in 2013 (see When politicians and bureaucrats decide the science).

The Hamilton City Council consultation also showed an extreme naivety in the Council’s willingness to ignore the established science. I wonder what approach they would have taken if the NZ Fluoridation Review had been available at the time?

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Social media and science – the problems and the challenge

Social media – Facebook, Twitter, etc., – are a challenge for science.  Often considered frivolous or at least not serious, they are tempting to ignore. But it seems that many anti-scientific or pseudoscientific ideas a promoted by social media. What’s more, these new social media are very effective at promoting messages, especially in areas of social health, so we ignore the media at our peril. Social media are a fact of modern life and if we can’t beat them, perhaps we should use them ourselves. These are the messages I got from a recent study of the way public health misinformation is promoted via social media. The paper is:

Seymour, B., Getman, R., Saraf, A., Zhang, L. H., & Kalenderian, E. (2015). When Advocacy Obscures Accuracy Online: Digital Pandemics of Public Health Misinformation Through an Antifluoride Case Study. American Journal of Public Health, 105(3), 517–523.

Although limited to an anti-fluoride Facebook case study I believe that the findings are also applicable to other anti-scientific movements like anti-vaccination and climate change denial. Here are some of the findings in the paper.

Anti-fluoride Facebook groups are highly connected

The connectedness within and between anti-fluoride networks was measured to get an idea of their social influence. networks Facebook “friend” connections between members within groups and between groups was very common and overall the study sample showed a significantly higher degree of connection than in Facebook overall. This is probably the result of group members having similar ideology or other traits leading to a desire to form social connections. Social influences lead to group shaping of individual attitudes and behaviours related to health and not reliance on expert findings.

Social diffusion of scientific misinformation

Using an original source article the authors followed posts about the article to determine the degree of social diffusion. They found 60% of the time a reader would have to follow 2 to 3 links to arrive at the original source with such a search failing 12% of the time. This demonstrated that:

“on average, there was a high risk that antifluoride Facebook group members engaged in posts about the article would be forced to navigate through multiple pages to locate the original post or would never succeed in locating it at all, greatly increasing the likelihood for the spread of misinformation and misrepresentation of the scientific article’s content.”

Although not detailed in the paper I believe that key sources of primary information for such social networks is very often articles in the “natural” health or alternative health magazines and websites which have already misinterpreted and misreported the scientific literature.

Engagement and sentiment

The levels of engagement and sentiment of the most influential posts were analysed:

“to explore the user experience with social diffusion of information and to determine how these posts could potentially influence group member attitudes and behaviors. Considering the distance between reference posts and the original source, this is particularly important.”

The figure below illustrates their finding for  the 2 most influential posts in the social diffusion map. Interestingly:

“The most frequent type of comment about the posts and the type of comment that received the most engagement were the science-based comments . . . Science-based comments overall received a positive (profluoride) total sentiment score of 36 (additive over all comments), whereas all other types of comments received an overall negative (antifluoride) sentiment score of –47.”

Seymour-3

“These results demonstrate that the user experience, when engaging with these influential posts, is just as likely to be negative and irrelevant to the original source as it is to be positive and reference scientific information (accurate or not). Our results demonstrate a high probability (1 in 2 chance) of encountering negative and non-science-based information about fluoride that is unrelated to the original peer-reviewed scientific publication under discussion.”

Social media overriding traditional health communication?

The new social media have given a new power to social networks:

“Historically, naturally limiting factors such as geography and communication barriers inhibited opportunities for strengthening networks with outlying views. Risky behaviors as a result of shared moral evaluations, such as opting out of  recommended childhood vaccination schedules and rejecting fluoridation, reverberated in existing small networks without necessarily scaling to dangerous magnitudes.”

But:

“online social networking allows greater connectivity among networks through the increased visibility of group behavior; previously nonnormative behaviors can thus become normative through the use of social media.”

Now that minority ideas and behaviours have an online market they can spread through confirmation bias and the expanding social networks, and the strong ties in the networks reinforce the sentiments behind the spreading messages.
The group thinking and the “silo,” even protective,  nature of social networks means that:

“Expert opinion grounded in evidence that contradicts the sentiments embedded in a socially diffused message will be quickly rejected; acceptance of this contradictory information would be socially detrimental to the network, challenging its very identity. Thus marks the beginning of digital pandemics of misguided and incomplete health information in which evidence becomes entirely secondary to the sociology of the networks diffusing it.”

Are there lessons here for pro-science groups?

The findings of this research will strike a chord with sceptics and others who fight anti-evidence-based approaches to health online. They will easily recognise the social norms of such groups which leads to rejection of any attempt to inject a pro-science discussion. They will have experienced the put-downs and banning or blocking used to reinforce and protect those within-group social norms.
But should we be drawing lessons from this? The authors conclude:

“Traditional vertical health communication strategies, such as broadcast diffusion through peer review publication and media reporting, may no longer be effective because of the existence and viral potential of social diffusion”

Perhaps we have to accept that:

“the sociology of networks is perhaps just as influential as, if not more influential than, the information content and scientific validity of a particular health topic discussed within and between certain networks via social media.”

Rather than trying to beat this new technology perhaps we should try to use it ourselves more effectively. The authors suggest:

“Empirical social strategies for health communication should focus not only on high-quality digital information production and dissemination but also on socially targeted and custom-designed messaging that conforms to the norms and values of specific target networks rather than challenging them. Developing an appreciation for the sociology of target groups could assist public health experts in increasing influence in problem networks and could provide the tools to predict, prevent, or reverse digital pandemics.”

The internet has forced changes on the traditional methods of information dissemination in other areas so it is really not surprising to expect it to change scientific and public health communication. As the authors say in their final words:

“The public nature of social media is at once a barrier to accurate information flow online and a tremendous opportunity for public health research, innovation, and intervention. In an age when negative digital pandemics can go viral, public health communication management strategies must go social.”

See also: An emerging threat of “digital pandemics”- lessons learned from the anti-vaccine movement
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Open letter to Lisa Hansen on NZ Fluoridation Review

Dear Lisa,

There are mistakes and misinterpretations of the scientific literature in your recent open letter to Sir Peter Gluckman and Sir David Skeggs. The letter also misrepresents the NZ Fluoridation Review (Eason et al., 2014) and the Fluoride Free NZ (FFNZ) report criticising that review. It gives the latter report more credibility and status than it deserves.

I am responding with an open letter of my own because I think the mistakes and misrepresentations need correction. I hope you receive my critique with the respect for the scientific openness,  criticism and healthy discussion you assert in the last paragraph of your letter. That certainly describes my approach and in that light I offer you a right of reply on my blog to this open letter.

First I consider some aspects of the way you present the NZ Fluoridation Review and the FFNZ report.

Citing the NZ Fluoridation Review

You generally cite Health Effect of water fluoridation: A review of the scientific evidence (Easton et al., 2014) as  the “Gluckman/Skegg report.” I realise you did this because your clients, and particularly the Fluoride Free NZ activist group, have adopted that terminology. It is however disrespectful to the real authors of the review. Such reports are not usually attributed to the heads of institutes or organisations.

Nature of the NZ Fluoridation Review

You unfairly compare Easton et al., (2014) to other major reviews in terms of cost, time taken, processes and the publication period reviewed. You are simply citing the activist FFNZ report which set out to discredit the NZ Fluoridation Review in any way possible.

The Fluoridation Review describes its approach in this way:

“Several previous rigorous systematic reviews were used as the basis for this analysis, and literature searches in Medline, EMBASE, the Cochrane library database, Scopus, and Web of Science were undertaken to identify subsequent studies in the peer-reviewed scientific literature. Alleged health effects from both the scientific and non-scientific literature were considered, and many original studies relating to these claims were re-analysed.” [My emphasis].

The Review’s purpose was not to duplicate the previous extensive reviews on this subject. It instead summarised them and reviewed later research. In other words the goals were simpler and less costly. (Costs were in any case determined by the local bodies which commissioned and, together with the Ministry of Health,  paid for the review.)

The FFNZ comparison is disingenuous.

The FFNZ Report.

You promote the inaccurate self-description of the FFNZ report (Scientific and Critical Analysis of the 2014 New Zealand Fluoridation Report) as “international peer reviewed.” That is the impression FFNZ attempts to convey  but it is dishonest – all the authors and “peer-reviewers” are connected with, or work for, Paul Connett’s Fluoride Action Network and similar activist organisations in the US or NZ. I illustrate some of the links in the figure below taken from the blog article The farce of a “sciency” anti-fluoride report.

I have provided an in-depth analysis and critique of the FFNZ report in a series of blog articles which are available in a single PDF document (Fluoridation is safe and effective: A critique of Fluoride Free NZ’s criticism of The NZ Fluoridation Review).

Now, the substantive issues you raise in your open letter.

Endemic fluorosis, community water fluoridation and IQ

Up front we must be clear about the situations behind the various scientific studies on the issue of fluoride and IQ.

So far, the only study  directly relevant to community water fluoridation (CWF) is that of Broadbent et al., (2014). This studied populations in the Dunedin region over a long time period. Notably you do not refer to this study, despite its extensive nature and relevance to the issue at hand. In  fact you seem unaware of the research as you claim in your letter that the “impact on IQ from water fluoridation at between 0.7 and 1 ppm” is “as yet unmeasured!”

The studies you do cite (mainly Choi et al., 2012) are from areas of higher fluoride consumption. Most of the studies were from areas of endemic fluorosis – mainly in China. This means that the findings cannot simply be transferred to areas like NZ.

Choi et al., (2012) are clear about the criteria used for choice of studies in their metareview. They say:

“We specifically targeted studies carried out in rural China that have not been widely disseminated, thus complementing the studies that have been included in previous reviews and risk assessment reports.”

And

“Opportunities for epidemiological studies depend on the existence of comparable population groups exposed to different levels of fluoride from drinking water. Such circumstances are difficult to find in many industrialized countries, because fluoride concentrations in community water are usually no higher than 1 mg/L, even when fluoride is added to water supplies as a public health measure to reduce tooth decay.”

This is why the Choi et al., (2012) meta review is not directly relevant to CWF.

Choi et al., (2012) not relevant to CWF.

I can illustrate the difference between that situations reviewed by Choi et al., (2012) and the New Zealand situation where CWF is common using dental fluorosis data from the recent paper of Choi et al., (2015),  Our Oral Health (2010) and Beltrán-aguilar & Barker (2010) (see Water fluoridation and dental fluorosis – debunking some myths).

There is very little severe or moderate dental fluorosis in NZ and USA. But it is very common in the area studied by Choi et al., (2015) which is probably typical of the areas reviewed by Choi et al., (2012) and the Indian paper you cite (Saxena et al., 2012). Unfortunately most of the studies reviewed by Choi et al., (2012) are of poor quality (see below) and do not include data for many possibly confounding factors like severe dental fluorosis, pesticide use, etc.).

So – clearly different situations.

The metareview of Choi et al (2012) was a metareview of studies from higher fluoride areas – not a metareview of studies from all areas, or studies from areas where CWF is common. Their review is not directly applicable to situations where CWF is considered, like NZ and USA.

The authors have stated this themselves:

“These results do not allow us to make any judgment regarding possible levels of risk at levels of exposure typical for water fluoridation in the U.S. On the other hand, neither can it be concluded that no risk is present.”

Note: I have suggested (Perrott 2015) that the small cognitive deficits report by the Choi et al., (2012) could be caused by severe dental fluorosis, and not directly caused by chemical toxicity. (I discuss this further below.) This is consistent with the results of Choi et al., (2015) who observed a significant relationship of cognitive deficits to severe/medium dental fluorosis but did not find a significant relationship with the fluoride concentration of the drinking water.

I believe researchers studying IQ effects in areas of endemic fluorosis should consider this hypothesis.

The “error” in the NZ Fluoridation Review

Your open letter concentrates mainly on an “error” in the NZ Fluoridation Review. This “error” was little more than a “typo,” occurred only in the executive summary (the body of the review reported the science correctly), and was corrected by the authors when brought to their attention. They also corrected at least one other error at the same time. I have discussed this in Did the Royal Society get it wrong about fluoridation?

Any publishing author is well acquainted with the problems of typos and similar errors. Despite the best proof-reading of drafts one inevitably finds some errors only after publication. (An example of Murphy’s Law, I guess.) This error has only become an issue because of the intention of activist organisations who wish to discredit the review.

It is worth noting that the Harvard University press release reporting the research concerned made exactly the same error and acknowledged and corrected it when pointed out. The current version now says:

“The average loss in IQ was reported as a standardized weighted mean difference of 0.45, which would be approximately equivalent to seven IQ points for commonly used IQ scores with a standard deviation of 15.*

** This sentence was updated on September 5, 2012.”

Yet, you, FFNZ and their associates do not criticise Harvard University!

Your mistaken description of error.

First, I will stress again that discussion of this “error” refers to the work of Choi et al., (2012) and areas where fluorosis is most likely endemic. That research does not deal with CWF or the situations where drinking water fluoride concentrations are that low.

The slide below, from a presentation made by Xiang (2014) at Paul Connett’s last conference in Washington, gives an idea of the situation in areas where these studies were made. Xiang is the author of several of the papers reviewed by Choi et al (2012) and commonly used by anti-fluoride activists in arguing against CWF.

This is clearly a different situation to New Zealand.

What did Choi et al (2012) actually report?

They report in their abstract “The standardized weighted mean difference in IQ score between exposed and reference populations was –0.45.” This is a standard deviation resulting from their analysis of 27 studies with different methods and quality of data. It is not a difference in IQ score.

This approach was necessary because the different studies reviewed had different IQ scales, different measurement methods and different levels of variation in the data. They standardised the differences by expressing them as a fraction of the standard deviation for each study. A mean value over all studies was determined, weighting the contribution from each study according to the precision of the IQ measurements.

Mistakenly, Harvard University and the NZ Review summary originally described this as an IQ score difference instead of SD. (Note – this mistake was not in the body of the NZ Fluoridation Review). In fact many readers were confused as the statistical process used by a Choi et al (2012) was not sufficiently well explained from a lay person’s viewpoint and they had to publish an extra explanation later (Choi et al., 2013).

Going from a standardised weighted mean difference value to a difference in IQ points.

Standard deviation is a function if variation in data so it is wrong to assume a value for all situations. It will be different for different sets of data.

The standardised weighted mean difference value of 0.45 has meaning because we know it represents less than half of one standard deviation so it indicates how it compares with measurement error. Many people have equated the difference of 0.45 to 7 IQ points. However, Choi et al., (2012)  did not report a difference of 7 you claim. This value came out of the explanation in Choi et al., (2013) in their response to a letter to the editor. They provided an example for a commonly used IQ scale normalised against a theoretical bell curve:

“For commonly used IQ scores with a mean of 100 and an SD of 15, 0.45 SDs is equivalent to 6.75 points (rounded to 7 points).”

This cannot simply be translated to any other IQ scale. For example these values would be inappropriate for the IQ scale used in Saxena et al., (2012)  study you refer to later in your letter.

The significance of the 0.45 standard deviation decrease in IQ points.

It is easy to throw around values of 7 and 15, as you do, but what is the significance of the result (for areas of endemic fluorosis – let’s not forget this study is not directly relevant to CWF). Choi et al., (2012) themselves warn that a decrease of 0.45 standard deviation “may seem small and may be within the measurement error of IQ testing.”

All this says is that many data sets, especially those with high variability, may not show a difference between children from high and low fluoride areas because the difference measured by Choi et al., (2012) is relatively small. In saying that I am not trying to deny any significance at all to their results. However, it is provisional and, as they say, it needs further confirmation. I think two points must be made here:

  1. The metareview was purposely biased towards studies from China and high fluorosis areas – many of which show endemic fluorosis. It is not directly relevant to the issue of CWF;
  2. The articles reviewed were in themselves mostly of poor quality, did not consider confounding factors and were often very brief (see figure). Not the fault of Choi et al., (2012) and hardly a surprising situation for the regions of interest, but this does help put the value of 0.45 standard deviation into context. It is, as yet, really only provisional.

Histogram showing size of the reports reviewed by Choi et al., (2012) from 

Your claim the Fluoridation Review misrepresented Choi et al (2012) in a specific quote.

Choi et al., (2012) themselves say:

“The estimated decrease in average IQ associated with fluoride exposure based on our analysis may seem small and may be within the measurement error of IQ resting.”

This is a valid assessment because the mean difference they observed amounted to only 0.45 of a standard deviation which can be related to measurement error.

The Review refers to this text (and quotes as section of it) as follows:

The authors themselves note the difference is so small that “it may be within the measure tn error of IQ testing.”

I really don’t see any misrepresentation there. The authors did note that the difference was small compared with measurement error.

In summary I reject your criticisms on this issue for these reasons:

  1. You have relied for claims on a metareview of studies from areas of endemic fluorosis. A study reviewing reports of mainly poor quality and which the authors had described as not relevant to areas using CWF.
  2. You misrepresent correction of the small mistake as a change in recognition of the science or a “misreading of the available evidence.” There was no change as the science was correctly reported in the body of the review – the mistake occurred only in the summary. Others have made similar  mistakes – including Harvard University in their press release.
  3. You repeatedly refer to an IQ point differences of 7 without at any time considering how significant this value is compared with the measurement errors.
  4. You imply that this issue was not thoroughly addressed, which is wrong as it was discussed in the body of the review. Correction of the mistake in the summary is all that was required.

But, I stress again, whatever the significance of the small IQ differences reported for areas with endemic fluorosis in these studies they are not relevant to areas like NZ where no IQ deficits have been reported for CWF. In fact, quite the opposite (Broadbent et al., 2014).

Claims of neglected evidence

You  express concern “relevant evidence” was neglected by the authors of the review.

You refer to 2 papers:

1: Cheng and Lynn (2013) and a study “(referred to by Cheng and Lynn).” However, you do not attempt to explain what this paper contributes. The journal (it is in Mankind Quarterly) is not one normally considered for publishing scientific papers and is extremely difficult to access. My reading of the paper indicates nothing new – in fact it is a repetition of the data from the Choi et al., (2012) paper (which I find strange as it doesn’t even cite that paper).

Why do you wish Mankind Quarterly to be cited? Published by the Ulster Institute for Social Research (and not a scientific body), Wikipedia describes it this way:

“It has been called a “cornerstone of the scientific racism establishment” and a “white supremacist journal”, “scientific racism’s keepers of the flame”, a journal with a “racist orientation” and an “infamous racist journal”, and “journal of ‘scientific racism'”.

2: The cross-sectional study by Saxena et al., (2012). I agree this wasn’t included – but then again it is not relevant to CWF. The study considered situations where drinking water F concentration was greater than 1.5 ppm.

Unfortunately the images you reproduce could give a misleading impression. The linear plot in your figure was actually for the relationship between urine F concentration and drinking water concentration.

The plot for intelligence grade does not look so impressive (see figure).

Saxena

Saxena et al., (2012 ) do show an increase in mean intelligence grade (corresponding to a decrease in IQ) for the increasing concentration ranges. (You should perhaps note your reference to a standard deviation of 15 in such studies is clearly irrelevant to this study). They admit to several limitations in their study. We can agree with their assertion there is a “need for a more careful evaluation of the effect of fluoride on intelligence.” But given the endemic fluorosis in the area they studied, and in the areas of the studies reviewed by Choi et al., (2012) and studied by Choi et al., (2015) I suggest this is only relevant to such areas. I stress –  no such IQ differences were observed in areas where CWF is used (Broadbent et al., 2014).

I am aware of a number of other studies reporting cognitive deficits in areas of endemic fluorosis – suggesting IQ may well be a topical area of research in such areas. The NZ Fluoridation Review may not have cited these – precisely because they are not relevant to our situation.

However, I will reproduce some data from one of them (Sudhir et al., 2009) because it is directly relevant to the next topic. These authors did see increasing cognitive deficits with increasing concentration of F in drinking water. But they also saw a strong relationship between cognitive deficit and severe dental fluorosis (see figure below).

Sudhir

In this study IQ grade 5 is “intellectually impaired” and grade 3 is “intellectually average.”

Severe dental fluorosis and cognitive deficits

I stressed at the beginning of this letter that these IQ studies have all (except for Broadbent et al., 2014) concentrated on areas of endemic fluorosis. Children in these areas show high incidence of severe dental fluorosis and this is quite different to New Zealand (see the second figure in this letter). It is also noteworthy that Choi et al., (2015) chose to extend their work in an area of endemic fluorosis (in a Chinese village) and not an area of the USA where CWF is common. Maybe they recognise this is a problem for areas of endemic fluorosis and not for areas using CWF.

Unfortunately researchers like Choi et al., (2015) have limited their working hypothesis only to chemical toxicity. But, dental defects are known to cause decreased quality of life and this could be translated into learning difficulties and reduced IQ scores. In a recent article I suggested these researchers widen their considerations to including the hypothesis that severe dental fluorosis, in itself, could be a cause of cognitive deficits simply because of the effect of physical anomalies and appearance on IQ (see Perrott 2015).

This is, after all, consistent with their findings that cognitive deficits were significantly related to incidence of severe/medium dental fluorosis but not to the F concentration in the drinking water.

Other oral defects like bad dental decay are also known to cause a reduced quality of life and may lead to learning problems and cognitive deficits. While severe dental fluorosis is a problem in  areas of endemic fluorosis it is not here. I suggest you worry more about possible IQ effects of tooth decay than any due to fluoride in our drinking water.

You are just scaremongering with your flight of fancy suggesting that “institutionalizing the additional proportion of the population due to mental deficiency” should be considered as a cost against CWF. One could more sensibly say that in NZ the quality of life and possible cognitive deficits arising from dental decay should be considered as a cost against opposition to CWF.

Conclusion

Your letter is part of an ongoing campaign by New Zealand anti-fluoridation activists like FFNZ and New Health NZ to discredit the NZ Fluoridation Review. New Health NZ is part of the NZ Health Trust, a well-funded lobby group for the “natural”/alternative health industry in New Zealand. It campaigns on issues like fluoridation, vaccinations and “chemtrails” (see Who is funding anti-fluoridation High Court action? and Corporate backers of anti-fluoride movement lose in NZ High Court).

On the surface your complaint about the mistake in the summary of the NZ Fluoridation review is at least churlish. Especially as it was corrected when brought to the authors’ attention and there was no mistake in the body of the review. Despite the same mistake in the original version of Harvard University’s press release on the research neither you nor your colleagues in the NZ anti-fluoride movement have complained to Harvard University.

One would have though the correction of the mistake would have pulled the rug out from under the anti-fluoridation critics but you have unjustly tried to use the original mistake to argue that the authors of the NZ Fluoridation Review misunderstood or misrepresented the science. In fact, the misrepresentation comes from you and your anti-fluoridation colleagues as the study you seem to pin all your arguments on was made in areas of endemic fluorosis,  (mainly in China) and has no direct relevance to New Zealand CWF.

New Zealand health professionals and members of local bodies should see your complaint for what it is – part of the ongoing activist campaign against CWF. These decision makers are justified in the confidence they have in the NZ Fluoridation Review.

Yours sincerely,

Dr Ken Perrott

References

Beltrán-aguilar, E. D., & Barker, L. (2010). Prevalence and Severity of Dental Fluorosis in the United States , 1999 – 2004 (pp. 1999–2004).

Broadbent, J. M., Thomson, W. M., Ramrakha, S., Moffitt, T. E., Zeng, J., Foster Page, L. A., & Poulton, R. (2014). Community Water Fluoridation and Intelligence: Prospective Study in New Zealand. American Journal of Public Health, 105(1), 72–76.

Cheng, H., & Lynn, R. (2013). The adverse effect of fluoride on Children’s intelligence: A systematic review. Mankind Quarterly, 53, 306–347.

Choi, A. L., Sun, G., Zhang, Y., & Grandjean, P. (2012). Developmental fluoride neurotoxicity: A systematic review and meta-analysis. Environmental Health Perspectives, 120(10), 1362–1368.

Choi, A. L., Grandjean, P., Sun, G., & Zhang, Y. (2013). Developmental fluoride neurotoxicity: Choi et al. Respond. Environmental Health Perspectives, 121(3), A70.

Choi, A. L., Zhang, Y., Sun, G., Bellinger, D., Wang, K., Yang, X. J., … Grandjean, P. (2015). Association of lifetime exposure to fluoride and cognitive functions in Chinese children: A pilot study. Neurotoxicology and Teratology, 47, 96–101.

Eason, C., & Elwood, JM. Seymour, Thomson, WM. Wilson, N. Prendergast, K. (2014). Health effects of water fluoridation : A review of the scientific evidence (p. 74).

Fluoride Free New Zealand. (2014). Scientific and Critical Analysis of the 2014 New Zealand Fluoridation Report

Hansen, L. (2015). An open letter to the Prime Minister’s Chief Science Advisor and to the President of the Royal Society of New Zealand.

Ministry of Health. (2010). Our Oral Health Key findings of the 2009 New Zealand Oral Health Survey. Wellington, Ministry of Health.

Perrott, K. W. (2015). Severe dental fluorosis and cognitive deficits. Neurotoxicology and Teratology.

Saxena, S., Sahay, A., & Goel, P. (2012). Effect of fluoride exposure on the intelligence of school children in Madhya Pradesh, India. Journal of Neurosciences in Rural Practice, 3(2), 144–9.

Sudhir, K. M., Chandu, G. N., Prashant, G. M., & Reddy, V. V. S. (2009). Effect of fluoride exposure on Intelligence Quotient ( IQ ) among 13-15 year old school children of known endemic area of fluorosis , Nalgonda District , Andhra Pradesh . JOURNAL OF THE INDIAN ASSOCIATION OF PUBLIC HEALTH DENTISTRY, 2009(13), 88–94.

Xiang, Q. (2014) Fluoride and IQ research in ChinaKeynote Address at FAN’s 5th Citizens’ Conference on Fluoride.