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Jul/Aug 2001: Chris
Holdcroft
BRIEF ANALYSIS OF
YORK REVIEW
D.M.F.T. Dental Studies for
U.K. Government 2000
By Chris Holdcroft - U.K.
“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:-
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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!).
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’ 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.
N.B. 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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