Tag Archives: Xiang

Anti-fluoride authors indulge in data manipulation and statistical porkies

Darrell Huff & Irving Geis wrote a classic book – How to Lie With Statistics. They outline various ways data can be presented to give the wrong story. However, there is an even more naive use of statistics to misrepresent data – just declare that a relationship is statistically significant, don’t show any data or statistical analysis.

Unfortunately, many people are fooled by the use of those magical words – “statistically significant.”

I suppose the lay person could be excused – although it would pay even them to be a bit more sceptical about such claims. But it seems that even some “scientific” journals, or perhaps inadequate peer reviewers, can be fooled by those magical words. Here is an example in the paper by Hirzy et al., (2015) in the journal Fluoride. (Yes, I know, this journal is well known for its anti-fluoride stance and poor scientific quality but I would have thought the editor, Bruce Spittle,  would have picked this one up – even if they do not have an adequate peer review system. Perhaps the fact Spittle is one of the authors of the paper is a factor).

I critiqued the paper in my article Debunking a “classic” fluoride-IQ paper by leading anti-fluoride propagandists and have submitted a more formal critique to the journal (see – Critique of a risk analysis aimed at establishing a safe dose of fluoride for children.) But here I just want to deal with those magical words used in the paper – “statistically significant.”

Hirzy et al (2016) rely completely on data reported by Xiang et al., (2003) and claim they “found a statistically significant negative relationship between . . . .  drinking water fluoride levels and IQ.” Trouble is – you can search through the data presented by Xiang et al., (2003) and there is absolutely nothing to indicate a “statistically significant” relationship. Sure, that paper actually claims “This study found a significant inverse concentration-response relationship between the fluoride level in drinking water and the IQ of children.”  But there is no table or graphic presenting the individual data points and no statistical analysis for drinking water F and IQ. Rather surprising because Xiang et al., (2003) did present the individual data points for urinary fluoride and did present some results for statistical analysis of other relationships.

The trick behind the misleading use of Xiang’s data

However, what Xiang et al (2003) did do was separate their drinking water fluoride and IQ data into different ranges. This is a table of their result.

While group F was data for one village (Xinhuai) and the data in the other groups were for a separate village (Wamiao), there was no explanation of the criteria used for the groups – and the numbers in each group very tremendously. Over half the children (290 of the total 512) were in Group F and the size of the other groups seem to arbitrarily vary between 8 and 111.

This manipulation produces data which can be used to imply a statistically significant relationship. Do the statistical analysis for water F and IQ in the above table and sure you get a lovely straight line, a correlation of 0.96 and very significant statistically (p=0.003). But because of the manipulation, this says exactly nothing about the original data.

I will illustrate this by taking some data which Xiang et al (2003) did provide – for urinary fluoride and IQ. The data are illustrated in the figure below from the paper.

A statistical analysis of that data did show it was statistically significant – Xiang et al. (2003) cite a “Pearson correlation coefficient –0.174 , p = 0.003.” Now, that explains about 3% of the variance in IQ and I would have liked to see a similar analysis for water F as other workers have usually found weaker relationships for water F than for urinary F.

But let’s try using the manipulation of Xiang et al (2o03) and Hirzy et al (2016) to make the relationship between urinary F and IQ look a lot better than it is. I used a software tool to extract data from the figure – it didn’t extract all the points (264 out of a total 290) because of overlaps but statistical analysis of my extracted data gave a Pearson correlation coefficient of 0.16, p=0.010. Very similar to that reported by Xiang et al., (2003).

The tricky manipulations

I have absolutely no idea why Xiang et al., (2003) used different group sizes – so, to be fair, I have divided my extracted data into 6 groups of 44 pairs each (after sorting them into order based on urinary F) to produce the following table.

Urinary F IQ
A 1.79 105.57
B 2.30 89.45
C 2.30 77.72
D 2.69 68.58
E 2.48 56.25
F 2.69 40.10

This produces a lovely graph:

But, just a minute, I can get a better graph if I sort  the data according to IQ instead of urinary F:

But why stop there. If I choose different group sizes – remember Xiang et al., (2003) had groups ranging from 8 to 250 in size – I am sure I can get an even better presentation of the data.

TBut these graphs look far better than the one presented in Xiang et al (2003) for urinary F. We have taken data where the urinary F data explains only about 3% of the variance in IQ and produced graphics implying it “explains” up to about 75% of the variance. And we could “explain” more with a bit of extrra manipulation.


Data manipulation like this doesn’t change the fact that while the relationship between urinary F and IQ is statistically significant it only explains about 3% of the variance in IQ. This means that other factors, or confounders, should be considered – and when they are it is likely the significant relationship of IQ to urinary F would disappear.

Although Xiang et al., (2003) did not provide any statistical analysis to support their claim there was a significant relationship between water F and IQ I am sure the relationship is similar to that for urinary F – maybe even worse. Manipulating the data by using a range of groups of different sizes has certainly made the data look a lot better – but it is completely misleading.

I think it shocking that the authors of the Hirzy et al., (2016) paper have used manipulated data in this way – first to claim that fluoride in drinking water has a major negative effect on IQ and secondly to use such massaged data to work out a “safe dose.”

Worse, the journal Fluoride, and its peer reviewers, should never have accepted this paper without querying the claim of a significant relationship between drinking water F and IQ.

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Debunking a “classic” fluoride-IQ paper by leading anti-fluoride propagandists


Three of the paper’s authors – Quanyong Xiang (1st Left), Paul Connett (2nd Left) and Bill Hirzy (far right) – preparing to bother the EPA.

Anti-fluoride groups and “natural”/alternative health groups and websites are currently promoting a new paper by several leading anti-fluoride propagandists. For two reasons:

  1. It’s about fluoride and IQ. The anti-fluoride movement recently decided to give priority to this issue in an attempt to get recognition of possible cognitive deficits, rather than dental fluorosis,  as the main negative health effect of community water fluoridation. They want to use the shonky sort of risk analysis presented in this paper to argue that harmful effects occur at much lower concentrations than currently accepted scientifically. Anti-fluoride guru, Paul Connett, has confidently predicted that this tactic will cause the end of community water fluoridation very soon!
  2. The authors are anti-fluoride luminaries – often described (by anti-fluoride activists) as world experts on community water fluoridation and world-class scientists. However, the scientific publication record for most of them is sparse and this often self-declared expertise is not actually recognised in the scientific community.

This is the paper – it is available to download as a pdf:

Hirzy, J. W., Connett, P., Xiang, Q., Spittle, B. J., & Kennedy, D. C. (2016). Developmental neurotoxicity of fluoride: a quantitative risk analysis towards establishing a safe daily dose of fluoride for children. Fluoride, 49(December), 379–400.


Co-author Bruce Spittle – Chief Editor of Fluoride – the journal of the International Society for Fluoride Research

I have been expecting publication of this paper for some time – Paul Connett indicated he was writing this paper during our debate in 2013/2014. FAN newsletters have from time to time lamented at the difficulty he and Bill Hirzy were having getting a journal to accept the paper. Connett felt reviewers’ feedback from these journals was biased. In the end, he has lumped for publication in Fluoride – which has a poor reputation because of its anti-fluoride bias and poor peer review. But, at last Connett and Hirzy have got their paper published and we can do our own evaluation of it.

The authors are:


Co-author David C. Kennedy – past president of the International Academy of Oral Medicine and Toxicology – an alternative dentist’s group.

Bill Hirzy, Paul Connett and Bruce Spittle are involved with the Fluoride Action Network (FAN), a political activist group which receives financial backing from the “natural”/alternative health industry. Bruce Spittle is also the  Chief Editor of Fluoride – the journal of the International Society for Fluoride Research Inc. (ISFR). David Kennedy is a Past President of the International Academy of Oral Medicine and Toxicology which is opposed to community water fluoridation.

Quanyong Xiang is a Chinese researcher who has published a number of papers on endemic fluorosis in China. He participated in the 2014 FAN conference where he spoke on endemic fluorosis in China.

xiang-Endemic fluorosis

Much of the anti-fluoridation propaganda used by activists relies on studies done in areas of endemic fluorosis. Slide from a presentation by Q. Xiang to an anti-fluoride meeting organised by Paul Connett’s Fluoride Action Network in 2014.

Critique of the paper

I have submitted a critique of this paper to the journal involved. Publication obviously takes some time (and, of course, it may be rejected).

However, if you want to read a draft of my submitted critique you can download a copy from Researchgate – Critique of a risk analysis aimed at establishing a safe dose of fluoride for children.  I am always interested in feedback – even (or especially) negative feedback – and you can give that in the comments section here or at Researchgate.

(Please note – uploading a document to Researchgate does not mean publication. It is simply an online place where documents can be stored. I try to keep copies of my documents there – unpublished as well as published. It is very convenient).

In my critique I deal with the following issues:

The authors have not established that fluoride is a cause of the cognitive deficits reported. What is the point in doing this sort of risk analysis if you don’t actually show that drinking water F is the major cause of cognitive deficits? Such an analysis is meaningless – even dangerous, as it diverts attention away from the real causes we should be concerned about.

All the reports of cognitive deficits cited by the authors are from areas of endemic fluorosis where drinking water fluoride concentrations are higher than where community water fluoridation is used. There are a whole range of health problems associated with dental and skeletal fluorosis of the severity found in areas of endemic fluorosis. These authors are simply extrapolating data from endemic areas without any justification.

The only report of negative health effects they cite from an area of community water fluoridation relates to attention deficit hyperactivity disorder (ADHD) and that paper does not consider important confounders. When these are considered the paper’s conclusions are found to be wrong – see ADHD linked to elevation not fluoridation, and ADHD link to fluoridation claim undermined again.

The data used by the Hirzy et al. (2016) are very poor. Although they claim that a single study from an area of endemic fluorosis shows a statistically significant correlation between IQ and drinking water fluoride that is not supported by any statistical analysis.

The statistically significant correlation of IQ with urinary fluoride they cite from that study explains only a very small fraction of the variability in IQ values (about 3%) suggesting that fluoride is not the major, or maybe not even a significant, factor for IQ. It is very likely that the correlation between IQ and water F would be any better.

Confounders like iodine, arsenic, lead, child age, parental income and parental education have not been properly considered – despite the claims made by Hirzy et al. (2016)

The authors base their analysis on manipulated data which disguises the poor relations of IQ to water fluoride. I have discussed this further in Connett fiddles the data on fluorideConnett & Hirzy do a shonky risk assessment for fluoride, and Connett misrepresents the fluoride and IQ data yet again.

Hirzy et al. (2016) devote a large part of their paper to critiquing Broadbent et al (2014) which showed no evidence of fluoride causing a decrease in IQ  using data from the Dunedin Multidisciplinary Health and Development Study. They obviously see it as a key obstacle to their analysis. Hirzy et al (2016) argue that dietary fluoride intake differences between the fluoridated and unfluoridated areas were too small to show an IQ effect. However, Hirzy et al (2016) rely on a motivated and speculative estimate of dietary intakes for their argument. And they ignore the fact the differences were large enough to show a beneficial effect of fluoride on oral health.


I conclude the authors did not provide sufficient evidence to warrant their calculation of a “safe dose.” They relied on manipulated data which disguised the poor relationship between drinking water fluoride and IQ. Their arguments for their “safe dose,” and against a major study showing no effect of community water fluoridation on IQ, are highly speculative and motivated.

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A Chinese study the anti-fluoridation crowd won’t be citing


Tooth brushing programme carried out in kindergartens in a Chinese rural area. Image credit: Supervised tooth brushing programme

Anti-fluoridation campaigners love to cite Dr Q. Y. Xiang to “prove” that community water fluoridation (CWF) can lower IQ. Trouble is – Xiang’s research on fluoride and IQ took place in an area of endemic fluorosis in China where drinking water fluoride levels were much higher than those used for CWF. That hasn’t stopped Paul Connett from making mileage out of Xiang’s data – even though the link between IQ and drinking water fluoride shown by Xiang’s data is very tenuous (see Connett fiddles the data on fluoride).

However, I suspect Connett and his activist organisation, The Fluoride Action Network (FAN), will be very quiet about the latest paper from this group. This is because the research they report supports the scientific consensus – in particular:

  • Fluoride at the concentration used in CWF does reduce tooth decay;
  • Fluoride at the concentration used in CWF does not cause the cosmetically undesirable forms of  dental fluorosis.

The paper is:

Xiang, J., Yan, L., Wang, YJ., Qin, Y., Wang, C. &  Xiang, QY. (2016). The effects of ten years of defluoridation on urinary fluoride, dental fluorosis, defect dental fluorosis, and dental caries, in Jiangsu province, PR China. Fluoride, 49(March), 23–35.

Yes, I know, it is published in Fluoride – which is hardly a credible scientific journal. And the lack of proper peer review sticks out like a sore thumb with mistakes in the text, poor data presentation and poor data statistical analysis.

Fluoride improves dental health

This is shown by data they collected in 2002 for two villages -Wamiao (a “severe endemic fluorosis village” with drinking water fluoride in the “range of 0.57 – 4.50 mg/L”) and Xinhuai (a “non-endemic fluorosis village” with drinking water fluoride in the “range 0.15 – 0.77 mg/L”). They combined the data for the 2 villages to produce the following graphic – from which they concluded that a “possible desirable range for the fluoride level for minimizing the prevalence of dental caries” . . .  [is] “approximately 1.5 – 2.5 m/L.” Considering this is just one study and has limitations the result is similar to the recommended fluoride level for CWF – 0.75 mg/L in the USA and 0.75 – 1.2 mg/L in New Zealand.

DMFT Xiang

OK, this is a poor graphic and I cannot see why they should have divided the data into the nine subgroups instead of statistically analysing the whole dataset (an indication of poor peer review by the journal?). But you get the picture. Dental decay declines as fluoride concentration in the drinking water in increased from near zero to about 1 mg/L.

CWF does not cause dental fluorosis

After 2002 the water sources used in the two villages changed:

“As a defluoridation project, water from two deep wells has been used as a tap water source of drinking water in Wamiao village since the beginning of 2003. The surface water in Yaohe river has been used as a tap water source in Xinhuai village since 2009.”

The current dental fluorosis study occurred in 2013 when the fluoride concentrations in both villages were in the range 0.85 – 0.95 mg/L. This is similar to the levels used in CWF.

In 2013, the researchers found very low levels of total dental fluorosis in both villages (3.1% in Xinhuai and 8.8% in Wamiao – no significant difference). They also measured “defect dental fluorosis” – a Chinese classification which includes some “moderate” dental fluorosis and all “severe dental fluorosis as diagnosed by Dean’s criteria (see  Water fluoridation and dental fluorosis – debunking some myths and the image below).

The prevalence of “defect dental fluorosis” in 21013 was zero for both villages.

This contrast markedly with the situation in 2002 where the prevalence of total dental fluorosis was significantly higher in Wamiao village (89%) than in Xinhuai (4.5%). The prevalence of “defect dental fluorosis” was 39% in Wamiao but zero in Xinhuai (data from Xiang, et al., 2004).

The 2013 data reported in this paper confirm what I have said again  and again in  articles here. CWF does not cause the cosmetically undesirable forms of dental fluorosis – the “moderate” and “severe” forms, or the “defect dental fluorosis” in the Chinese classification). Anti-fluoride campaigners always misrepresent this data by quoting figures for total dental fluorosis and claiming the effects are those only seen with “moderate” and “severe” forms.

Paper’s take home message

The new water supply in these two villages has solved the dental fluorosis problem while also maintaining a fluoride concentration comparable to that used in CWF and helping support a low level of dental decay in children. The data support other findings (and the current scientific consensus) showing that CWF does not cause any cosmetically undesirable dental fluorosis but does help prevent tooth decay.