Cherry picking fluoridation data

Anti fluoridationists certianly go in  for picking cherries when the produce “evidence” to discredit fluoridation. Two anti-fluoridatioon actvists, Bruce Spittle and Russel McLean, did this in there opinion piece in the Otago Daily Times recently (see No consent given for fluoridation). In particular, they carefuly selected data from the Ministry of Health’s database on the oral health of children.

How to “prove” fluoridation ineffective

They claimed:

The efficacy of water fluoridation is modest.The Dental School staff referred to the 2009 New Zealand Oral Health Survey which noted that in 2008, for all of New Zealand, the 5-year-olds in fluoridated areas had a percentage caries-free rate of 58.7% compared to the rate of 55.0% for those in non-fluoridated areas. However, the 2011 figures show little difference, with the rate for fluoridated areas being 59.91% and that for non-fluoridated areas being 59.18%.

In this case, while they chose the total data set, they selected just 2 years (2008 and 2011), selected only one age group, considered just “percentage caries-free” and ignored the data for “decayed, missing and filled teeth,” and also ignored the data for Maori (important because these show the influence of social and economic deprivation).

I looked at the whole data set in my article Fluoridation – it does reduce tooth decay. So I will just repeat a few of my data plots from that article toi show the effect of cherry picking. The plots of the data below give an idea of variability and trends. They also show the influence of social and economic deprivation is long-term. (Click on the graphs to enlarge for details).

% CARIES FREE

MEAN DECAYED, MISSING AND FILLED TEETH

There could well be some story in the apparent reduction of the effect of fluoridation shown by the % caries free of 5 year olds but that has to be put into the context of the whole data set. It is dishonest to just select the small samples Spittle and McLean did – but of course you can see why they did select those years and restricted their comments to just 5 year olds and “% caries free.”.

How to prove fluoridation damages oral health

The Fluoride Free New Zealand Facebook page provides another example of cherry picking (see Waikato Dental Health Stats). In this case their “findings” were so ludicrous that you might have thought they would blush at presenting them. There are some mistakes in their data, but it tends to show that children had better teeth in the non-fluoridated areas than the fluoridated areas!

Well, they achieved this by cherry picking data for one year (2011) and one region (the Waikato). If we look at some of the data over the availabke time period (2002 – 2011) for Waikato, we can see why they cherry picked this region and year.

But, comparing the Waikato data with the total data in the previous figures we can see a greater variability from year to year. This variability makes any honest comparison very difficult – but it does give opportunities for creative cherry picking. (Yes, I have just “cherry-picked” the caries free data for 5 years old in this graph – but I am making a point).

Be careful of variation and cherry picking

The opportunities for cherry picking in a field like this are everywhere because of the variability. This is not like the data one gets in a carefully controlled laboratory experiment. We are dealing with a biological system – which introduces biological variability. But on top of that, it is also a social system which introduces an extra set of variability.

As an example, I was recently discussing with my granddaughter her new school in Hamilton. She told me that all her friends actually lived out-of-town. But the dental data will have recorded them as being from a fluoridated area because, at the time, Hamilton was fluoridated. Then there are problems of getting consistent evaluation from a large number of dental nurses. Differences in dietary intake, drinking of bottled water, etc., – the list goes on.

Some of this variation “evens out” when the data set is large (and of course has more influence when only part of the data set is chosen. Yes, it would be nice to control for all these social effects but in the real world one rarely gets the opportunity.

However, my point is that the variability introduced into this sort of data by biological and social effects provides ample opportunity for political activists to cherry pick data to support their own story – confirmation bias if innocent and dishonest misrepresentation if not.

So, it is easy to make claims one way or the other in the fluoridation controversy – and to find data to support these claims. But serious assessment of the claims requires critical evaluation of the data – something many people have no experience with.

This seems to have been the case with the Hamilton City Council who concluded from presentations heavily biased toward anti-fluoridationists that fluoridation of water supplies is not effective. But why should we expect city councillors to have the critical evaluation skills required to assess such data? They should never be put in the position of being asked to make scientific judgements in this way.

See also:

Similar articles on fluoridation
Making sense of fluoride Facebook page
New Zealanders for fluoridation Facebook page

Experts speak out on fluoridation

This is a letter to Dunedin City Councillors from 21 senior School of Dentistry staff. They believe that fluoridation of Dunedin’s water supply should be retained and expanded. As the Otago Daily Times headline puts it – Better oral health largely due to fluoridation.

I think it is a good summary which should be read more widely than in Dunedin. In the upcoming local body elections there will be referenda deciding on local fluoridation in Hastings, Whakatane and Hamilton. There are also campaigns against fluoridation in Auckland and Wellington with declared intentions to spread the campaigns even wider.

Here is the letter:

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In 1958, the Faculty of Dentistry requested the council to fluoridate the water supply of our city.

The Otago Branch of the Dental Association pledged its support of this request.

Our position remains unchanged after 55 years.

A debate surrounding community water fluoridation has recently surfaced again in Dunedin, and has received some coverage by local and national media.

We would, therefore, like to remind councillors of the strong case for fluoridation to continue in our city, and be expanded wherever feasible, including to unfluoridated areas of Mosgiel and areas covered by the Northern Water Scheme.

The New Zealand Ministry of Health has commissioned extensive reviews, which have led to development of ministry guidelines and statements on fluoridation.

These guidelines and statements are clear: community water fluoridation is effective and safe, and community water supplies should be fluoridated at 0.7-1.0 parts per million (ppm) wherever feasible.

The Australia New Zealand Food Safety Authority also approves the addition of fluoride to bottled drinking water, as it believes this is important for public health.

The US Centers of Disease Control estimate that for every $1 spent on water fluoridation, $38 is saved on tooth decay treatment, and named water fluoridation as one of the greatest public health improvement measures of the 20th century.

The World Health Organisation considers access to fluoride to be a human right.

Scientific evidence shows that there remains a very strong public health case for continuing and expanding the use of community water fluoridation, because it improves New Zealanders’ oral health and quality of life.

While the extent of tooth decay has reduced in recent decades, the disease remains more prevalent than other significant health conditions in New Zealand (such as asthma), particularly in unfluoridated areas and among disadvantaged New Zealanders.

The recent New Zealand Oral Health Survey found much less tooth decay in fluoridated than in non-fluoridated areas.

The argument that water fluoridation is no longer necessary due to better oral health in New Zealand is not correct.

In fact, the improved oral health we now enjoy in New Zealand compared to the past is in no small way a direct result of water fluoridation.

We forget that very few New Zealanders are affected by water-borne diseases, thanks to water chlorination.

If chlorination was not used, we would have more water-borne diseases.

If community water fluoridation ceased, the severity of tooth decay would increase again, back towards historical levels.

Fluoride is a naturally occurring substance which is present at varying concentrations in water.

It is even detectable at 0.1ppm in the water of the Rattray St ”Speight’s” spring.

Community water fluoridation is not just a matter of fluoride addition; rather, it is the adjustment of fluoride levels up (or even down) to an optimal effective level for the prevention of tooth decay.

Adjusting the background fluoride level (which is generally about 0.3ppm) to 0.7-1.0ppm has a significant effect of reducing tooth decay among people of all ages.

This is particularly important in New Zealand, as we are a country with very little in the way of a publicly funded ”safety net” for adults who cannot afford dental care.

We also now know that, rather than being a disease of childhood only, tooth decay continues through life.

We respectfully request that when councillors consider the fluoridation issue, they be aware of current Ministry of Health guidelines and statements on fluoride, and that when formulating strategy they consult relevant experts at the University of Otago and the Southern District Health Board who are familiar with the relevant peer-reviewed literature.

The opinions of those experts are strongly endorsed by the Otago Branch of the New Zealand Dental Association, the New Zealand Dental Hygienists’ Association and the New Zealand Dental and Oral Health Therapists’ Association.

The Otago Branch unequivocally supports the national Dental Association’s 2012 statement on water fluoridation.

We also advise councillors that anti-fluoridation arguments are often based on un-refereed internet resources or books that present a highly misleading picture of water fluoridation, rather than being based on objective science.

With this letter, we have included copies of an excellent Australian article from the journal Australia and New Zealand Health Policy, and the Victorian government publication Water fluoridation helps protect teeth through life.

Both are short, and are written for the benefit of public health officials.

We trust that the council will make the sensible public health decision to retain and expand community water fluoridation in our city.

See also

Other articles on fluoridation
Making sense of fluoride Facebook page.