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A collection of Critiques of the York Review

BRIEF ANALYSIS OF YORK REVIEW

By Chris Holdcroft


“Facts, or what a man believes to be facts, are always delightful ... Get your facts first, and ... then you can distort ’em as much as you please.” - Twain, quoted in Rudyard Kipling’s From Sea to Sea.


It has been demonstrated how the pro-fluoride lobby has managed to overcome a number of hurdles in their attempt to dispose of toxic fluoride wastes via public water supplies. They infiltrated and influenced Government, and consolidated. This was followed by using their influence within powerful circles to create a public health ‘need’ for fluoridated water.

The next stage was to ‘produce’ statistics based on badly designed studies to underpin their claim that drinking fluoridated water is effective in reducing tooth decay. Much has already been said, and written, about the earliest fluoridation trials and schemes. Despite being trumpeted as ‘successes’ by the pro-fluoride lobby, such schemes have often come in for severe criticism due to their bad design and assumptive conclusions.

A letter which condemns the presentation of dental health data comes from a statistician: Professor J N R Jeffers of Cumbria.

In early 1997, Professor Jeffers received a letter asking for his opinion of ‘dental health league tables’. These ‘league tables’ are produced annually for various age groups and give the number of decayed, missing and filled teeth (“dmft”), plus the fluoridation status, for each district health authority in the UK. They are normally published by the Government-sponsored pro-fluoridation propaganda machine, the British Fluoridation Society.

Professor Jeffers highlighted the inadequacies of such league tables:

I was interested in the league tables for 5-year and 14-year old children that you sent me a few weeks ago, principally because they are excellent examples of how not to present information - unless you are determined to distort that presentation in favour of a particular argument. I often use data sets of this kind as case studies for my students, and you may be interested to see the case study that I have prepared for these particular data.

As you will see, the way in which districts were chosen for fluoridation does not allow of any rational judgement about the effects - beneficial or otherwise - of the effects of fluoridation. There are too many other factors which are confounded with the allocation of districts to treated and untreated groups. The league tables would have you believe otherwise.”

Perhaps realising the poor value of dental health league tables, the pro-fluoride lobby has been thrown a lifeline by the publication of the NHS/CRD York Review of water fluoridation. In this review, a number of dmft studies were produced in an attempt to show that fluoridation was effective. But how good is this evidence?

On page 13 of the final report the following statement was made:

“Fifteen studies found a statistically significantly greater mean change in dmft/DMFT scores in the fluoridated areas than the non-fluoridated areas. The range of mean change in dmft/DMFT score was from 0.5 to 4.4, median 2.25 teeth (interquartile range 1.28, 3.63 teeth).”

The 15 (16 listed) studies used to reach this conclusion can be attributed to the following authors:

  • Beal (1981) Scunthorpe [F] / Corby, England
  • Guo (1984) Chung-Hsing New Village [F] / Tsao, Taiwan
  • Kunzel (1997) Chemnitz [F] / Plauen, Germany
  • Brown (1965) Brantford [F] / Stratford [Nat F] / Sarnia, Canada

NB. FOUR studies, not fifteen (or sixteen!) (Extra emphasis added!)

The overall conclusion must be that 50 years (or more) of research has failed to provide but a handful of sub-standard and questionable studies which do nothing to substantiate the claim that water fluoridation is effective.

However, the use of just four ‘complete’ (but mediocre) studies is hardly a foundation for such a bold claim:

[1] Beal [1981]. The areas chosen for comparison seem to be poorly matched despite the claims of the Author that the socio-economic factors were “similar”. Corby (non-fluoridated) is a deprived area but fluoridated Scunthorpe has a modest level of affluence (1991 census). It is therefore surprising that Dr Beal arrived at his conclusions;

NB. The D.M.F.T. has improved by up to 80% in 90% non-fluoridated U.K. between 1973-1993. (Source: Children’s Dental Health in the UK, 1993).

[2] Brown [1965]. This was a very poor study and open to abuse. In Brown’s own words he stated:

"... the recordings so far obtained indicated both a high treatment level and an apparently better oral hygiene status of the Brantford children when compared with the controls, and it is therefore suggested that caution should be exercised in the interpretation of the rates shown. The lack of a prefluoridation survey on a comparable basis is a further limiting factor in interpreting the results.” [Ecologist, vol. 16, no. 6, 1986]

This warning was made to NHS/CRD unit at York University but was obviously ignored. The Ecologist article further stated:

“In the 1955 Division of Medical Statistics, Ontario Department of Health, Province of Ontario, Canada, any fall in the dental caries rate of deciduous teeth in the control city of Sarnia was omitted, yet the percentage deduction there was 16 per cent, as compared with 18 per cent in the test city.”

[3] Guo [1984] and Kunzel [1997]. Little is known about these two complete studies though both have their defects. Neither adequately dealt with ‘confounding’ factors and Guo did not receive any marks for study design.

None of the above four studies controlled for confounding factors and yet it is known that there are a number of factors which can affect dental health statistics. When the author submitted to the review panel data on confounding factors which can affect dental health, they were rejected.

Another ‘faulty’ analysis by the NHS/CRD unit concerns the Hardwick (1982) study. The study indicated that after fluoridation, tooth decay went up in the fluoridated district but came down in the non-fluoridated district (thus indicating a negative association, with fluoridation):

There is also the question of sample size which varies between baseline readings and the final results. It is claimed that the SAME children were examined before and after - so why two different sample sizes?

To ‘rub salt into the wound’, the interpretation of this study was reversed to give a POSITIVE association with fluoridation when according to the figures it should have been NEGATIVE. The excuse given was that only ‘new’ decay was counted!


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