Errors
and Omissions in Experimental Trials - 1a
PHILIP R. N. SUTTON
D.D.Sc (Melb), L.D.S. (Vic.)
Senior Research Fellow, Department of Oral Medicine and Surgery
Dental School, University of Melbourne
D.D.Sc (Melb), L.D.S. (Vic.)
Senior Research Fellow, Department of Oral Medicine and Surgery
Dental School, University of Melbourne
MELBOURNE UNIVERSITY PRESS
First published in 1959
Second edition, enlarged, 1960
Printed and bound in Australia by
Melbourne University Press, Parkville N.2, Victoria
Registered in Australia for transmission by post as a book
London and New York: Cambridge University Press
Second edition, enlarged, 1960
Printed and bound in Australia by
Melbourne University Press, Parkville N.2, Victoria
Registered in Australia for transmission by post as a book
London and New York: Cambridge University Press
PREFACE TO THE SECOND EDITION
Soon after the publication of the
first edition of this monograph, in September 1959;
copies were sent, by the Australian Dental
Association, to the workers in charge of all the
studies considered. As a result, critical reviews
were published in the February 1960 issue of the
Australian Dental Journal. The New Zealand Dental
Journal of January 1960 also contained a critical
review. These have not indicated the necessity for
any modifications in Parts One and Two which are,
therefore, reprinted unchanged. However, in this
edition a Part Three has been added in which these
criticisms are reprinted, at length, and some
comments made. It is again stressed that in this
book consideration is limited to some aspects of
five crucial experimental trials of artificial
fluoridation. Results reported from "naturally
fluoridated" areas are not considered.
P.R.N.S.
Dental School, University of Melbourne
June 1960
Dental School, University of Melbourne
June 1960
PREFACE TO THE FIRST EDITION
Endorsements of the process of the
mechanical addition of fluorides to public water
supplies, with the aim of reducing the incidence of
dental caries, rely mainly on the results published
from five trials which were set up to test,
primarily, the efficacy of this process.
Important deficiencies in the
methods used were revealed during a preliminary
investigation of reports of these trials. Therefore
this study was undertaken in an attempt to answer
the question: Can the claims of considerable dental
benefits as a result of artificial fluoridation be
regarded as established, or are they based on an
unsound foundation.
P.R.N.S.
Dental School, University of Melbourne
February 1959
ACKNOWLEDGMENTS
Members of the Department of
Statistics, University of Melbourne, have given most
careful consideration to all the statistical matters
mentioned in Part One of this monograph they have
checked the computations in Part Two and have also
given advice regarding statistical matters mentioned
in Part Three. Their assistance is gratefully
acknowledged. Part One was published in the Medical
Journal of Australia, 1 February 1958, pages 139-40.
1 should like to express my thanks to my co-author,
and to the Editor of the journal for permission to
reprint the paper and also to the Editors of the
Australian Dental Journal and the New Zealand Dental
Journal for permission to reprint the book reviews
shown in Part Three. Extracts from Part Two were
presented at the fifteenth Australian Dental
Association Congress, Adelaide, 23-7 February 1959.
Professor Sir Arthur Amies and Dr Paul Pincus have
suggested improvements to the draft of Part Two, and
Miss H. N. Rankine, the Librarian of the Dental
School of the University of Melbourne, has given
valuable assistance. This investigation has been
supported by grants from the University of Melbourne
Research Fund.
PART ONE
SOME STATISTICAL OBSERVATIONS ON
FLUORIDATION TRIALS*
The suggestion that domestic water
supplies should be-fluoridated, with the aim of
partially preventing the development of dental
caries, has gained wide support, and moves are being
made in Australia for the widespread introduction of
this measure. Much confusion of thought clouds the
issue of the desirability, the method of action and
the safety of this process. This uncertainty is
reflected in two recent events. In November 1956, a
Reference Committee of the American Medical
Association (1957) stated that "there is a definite
need for a re-evaluation of the problem of
fluoridation",†
and in March 1957, after a public hearing, the
proposal to fluoridate the water supply of New York
was not put into practice (Nesin, B.C., personal
communication, 1957).
Apart from these considerations, an
examination reveals that there are aspects that call
for a very careful appraisal of the figures
presented in the reports of the experimental trials
which have been conducted in Brantford, Canada, and
in Grand Rapids, Newburgh and Evanston, U.S.A., and
upon the results of which proposals to fluoridate
domestic water are almost entirely based.
A preliminary survey of the methods
used, of the published figures and of the method of
their presentation discloses some disturbing facts.
Some of these are as follows. (i) In the clinical
examinations no attempt was made to devise a
randomization procedure, which would have eliminated
bias on the part of the examiners. However, the
necessity for such a precaution was recognized by
Ast, Bushel, Wachs and Chase (1955) in the
Newburgh-Kingston trial, when they instituted a
combined clinical and X-ray study eight years after
the commencement of the ten-year investigation. (ii)
No estimate was made of variability between
examiners, although in some studies several
operators were employed, some being changed from
year to year (Blayney and Tucker, 1948; Arnold, Dean
and Knutson, 1953); some of the examinations in
Kingston were made by two dental hygienists (Ast,
Finn and McCaffrey, 1950). Furthermore, there
appears to be no estimate of variability within the
examiner-that is, the variability of individual
examiners from inspection to inspection. (iii) The
importance of random variation in the DMF rate
(decayed-missing-filled permanent teeth rate) does
not appear to have been recognized, or else it has
been ignored. (iv) Bias is suggested by the
presentation of some results, so that the casual
reader may be misled (Ontario Department of Health,
1956).
* Reprinted from a paper
by Philip R. N. Sutton. D.D.Sc. (Melb.), L.D.S.
(Vic.) and Arthur B. P Amies, C.M.G., D.D.Sc. (Melb.),
F.R.C.S. (Edin.), F.R.A.C.S., originally published
in the Medical Journal of Australia, 1 February
1958. † In December 1957, the
American Medical Association endorsed the principle
of fluoridation, but that decision cannot affect the
facts which have been stated in this paper.
The following observations will
serve as illustrations.
1. In each of these studies it has been emphasized that the maximum benefits of fluoridated water are seen only in those subjects who have consumed it during the total period of enamel formation. Therefore, it would be expected that only a slight decrease (due to the possible topical effect of the fluorine) would be seen in the DMF rate between successive years during approximately the first six years of the project, until the first permanent teeth which had been completely formed under its influence had erupted, and that the advent of these "resistant" teeth would thereafter produce a greater drop in DMF rate between succeeding years. However, in the first three years of each project there is a marked relative fall in the reported DMF rate, particularly in the younger age groups; while in the six years-old group in Brantford the rate reached after ten years is no lower than it was after only four years of fluoridation, (Ontario Department of Health, 1956; Hutton, Linscott and Williams, 1956). It would appear that the results reported are not those which would be expected if the theory mentioned above is correct.2. In four of these studies (Hutton et al., 1956; Hill, Blayney and Wolf, 1956; Arnold, Dean and Knutson, 1953; Ontario Department of Health, 1956) the method of expressing changes in caries experience was the same. The final rate was subtracted from the baseline rate, and the difference was expressed as a percentage of the latter rate. It is obvious, therefore, that with this method, relatively small variations in the baseline values will produce substantial alterations in the percentage reduction obtained. For instance, in the seven-year-old children in Evanston, during the last five years reported, the increase in caries immune deciduous dentitions was 361 per cent, but for the whole of the nine-year period 1946-55 the increase was only 58 per cent "Hill et al., 1956). The authors claim that "difference between 1946 and 1955 rates is statistically significant" However, such a claim is not warranted, owing to the marked variation in the values observed in the intervening years. The effect of variations between years is seen in the six-yearold group in Brantford. By the use of this method of calculation the reduction in the DMF rate for the period 1944-50 was 82 per cent, but the apparent benefit had dropped to 52 per cent, a decrease of 30 per cent, after an additional two years fluoridation (Ontario Department of Health, 1956). An improved method of indicating relative changes in the DMF rate would seem to be desirable - in particular, one which would permit statistical tests to be applied.3. As an instance of the divergent results which can be reported by different examiners, those from the two independent trials in Brantford may be compared (Ontario Department of Health, 1956). The National Health and Welfare authors reported a reduction in the DMF rate in the six to eight years age group of 69 per cent from the inception of their examinations in 1948 to the 1954 results. However, in the same city, in the same age range and between the same years, the reduction in the DMF rate obtained by the City Health Department examiner was only 25 per cent, less than half of that claimed by the authors of the other study. The Health Department DMF figures for 1954 were given for individual age groups without statement of the number of children involved in each group. The 25 per cent reduction is based on a DMF rate obtained by simple averaging of the six, seven and eight year DMF rates. For 1948 the actual numbers of children are available (Hutton, Linscott and Williams, 1951). The uncertainty in the computed reduction of 25 per cent is most unlikely to account for the gross difference between it and the figure of 69 per cent quoted by the National Health and Welfare authors.4. In Table II of the Report of the Ontario Department of Health (1956) to the Ontario Minister of Health, the mean numbers of decayed or filled deciduous teeth are shown. In the column headed "% Reduction Since 1948", there are dashes Opposite the control cities of Sarnia and Stratford. These, surely, would lead the reader to suppose that no reductions had taken place in these cities, particularly as the footnote states that "the rates for Stratford, which has had natural fluoridation for 30 years, and Sarnia, which has no fluoride in its water, have remained about the same". However, in the nine to eleven years age group in Stratford there was a slight decrease of 5 per cent (by the use of the DMF rate reduction method common in these studies), and in Sarnia the same age group showed a decrease of no less than 16 per cent. One would like to know the reason for the omission of these figures, particularly as the latter reduction is almost as high as the 18 per cent claimed for children of the same age in the test city.Whilst we do not question the integrity of workers in this field, it must be pointed out that the evidence tendered in favour of fluoridation reveals two disturbing features. The first is that what must be essentially a statistical study does not appear to have been planned as such. The second is that even when sufficient information is presented, no comprehensive attempt at statistical evaluation has been considered.It is possible that a case for fluoridation can be solidly based, but until adequate statistical treatment of all the pertinent factors has been carried out and this would be quite a major undertaking the question should not be regarded as settled. In the meantime, claims concerning the amount of caries reduction are open to doubt.
PART TWO
FLUORIDATION TRIAL CONTROLS:
ERRORS, OMISSIONS AND MIS-STATEMENTS
INTRODUCTION
The fluoridation trials that were
conducted in the cities of Grand Rapids, Newburgh
and Evanston, in the U.S.A., and the two independent
ones in Brantford, Canada, are of more than ordinary
importance, because they constitute the main
experimental evidence which has led to the
introduction of this process as a public health
measure. The fluoridation hypothesis is "that a
concentration of about I part per million of
fluoride in the drinking water, mechanically added,
inhibits the development of dental caries in the
teeth of the users of the water" (Brown, McLaren and
Stewart, 1954b). In 1956 Nesin pointed out: "It must
be emphasized that the fluoridation hypothesis in
its entirety rests on a very narrow base of selected
experimental information. It is this very base which
is vulnerable to scientific criticism. And, it is
upon this very narrow base that the very impressive
array of endorsement rests like an inverted
pyramid."
The safety of artificial
fluoridation has been questioned by a number of
eminent authorities such as Hicks (1956) and
Sinclair and Wilson (1955). In 1955 Box stated: "It
is my considered opinion that the artificial
fluoridation of water supplies, on a wholesale
basis, should not be advocated or adopted until
fully sufficient findings show that there are no
harmful sequelae from a gingival or periodontal
standpoint."
However, these questions need be
considered only if the overall dental benefits of
fluoridation are demonstrated beyond reasonable
doubt, and are also found to be worthwhile from a
socio-economic point of view. No suggestion has been
made that fluoridation has other than dental
benefits.
It has been widely accepted that the
existence of marked dental benefits has been
established, and the literature abounds with
references to reductions of about 60 per cent in
dental caries as a result of fluoridation. However,
the published works contain little consideration of
the numerical data reported from these trials, as
distinct from mere statements of percentage
reductions in the caries attack rates.
A preliminary examination revealed
that reports of these studies contain errors and
show omissions, and statements made in regard to
results are not justified by published data;
therefore further study has been made of these
crucial trials. This study attempts to evaluate
their controls, and the discussion is limited to
examination of published reports of (i) method of
selection of control cities; (ii) their suitability;
(iii) the experimental and statistical processes
used in gathering and analysing the data (iv) the
results stating the dental caries attack rates; (v)
some comments made by the authors of these trials
(and by others) on these results.
The aim will be to investigate the
reliability of the results reported, to assess the
adequacy of the controls that were set up and to
evaluate the accuracy of the statements made
concerning the data obtained.
BASIC CONSIDERATIONS
Before discussing the procedure
adopted in each of these studies, several basic
matters that are of importance in a fluoridation
trial will be considered.
The necessity for controls.
Blayney and Tucker (1948) were correct in stating
that "A study of this nature must have an adequate
control." The necessity for such a procedure was
recognized by the authors of four out of five of
these studies. Cities with "fluoride-free" water
supplies were selected as controls, and comparisons
were made with towns which possessed water supplies
with a fluoride content obtained from natural
sources, which approximated the concentration which
has been called the "optimum" one (Dean, Arnold, Jay
and Knutson, 1950; Brown, 1951; Ast and Chase, 1953;
Hill, et al., 195 1). It is to be noted that
in the trial conducted in Brantford by the City
Health Department (Hutton et al., 1951) no
provision for controls was made.
Requirements of a control. In
an experiment such as the fluoridation of the water
supply of a city, whereby the whole of its
population is subjected to treatment (fluoridation),
it is necessary to obtain the control data from
subjects who live in a city or cities with
"fluoride-free" water supplies. In determining the
cities which are to participate in the trial, in
order to increase the sensitiveness of the
experiment, it is advantageous to employ ones which
are alike in as many respects as it is practically
convenient to consider. Of course, as Fisher (1951)
pointed out, "the uncontrolled causes which may
influence the result are always strictly
innumerable."
Because of the nature of these
experiments, three main points of similarity must be
considered and described. These are (a) the water
supply; (b) the climate; and (c) the dental caries
attack rates. Other factors, such as socioeconomic
status, are of less importance; their influence may
be reflected in the caries attack rates.
(a) In its statement of its official
policy on this matter, the American Water Works
Association (1949) said that the experimental
verification of the fluoride-dental caries
hypothesis "obviously necessitates the use of a
nearby "control" city with a water supply comparable
in all respects to that to which fluoride is being
added." The Association referred to "the possible
influence, on the fluoride potency, of other
chemical constituents of natural waters, insofar as
these and other variables may affect the action of
fluoride on the control of caries in a human
population." In 1942 Deatherage reported that "It is
these soft waters which cause the most severe
mottled enamel." Therefore, the fact that both the
test and the control city in a fluoridation trial
obtain their water from the same source does not
remove the necessity for a study of the composition
of the water. Dean, Jay, Arnold, McClure and Elvove
(1939) recognized this, stating, "the possibility
that the composition of the water in other respects
may also be a factor should not be overlooked. For
this reason it seems highly desirable that dental
caries studies should be accompanied by complete
chemical analyses of the dam waters, including a
search for the comparatively rare elements."
However, in none of these trials was the composition
of the water stated.
(b) The climate of a city is an
important factor in determining the average amount
of salts ingested from the water supply, because of
its influence on the volume of water consumed by
humans. Therefore, cities that are to be compared
should not only have water supplies that have a
closely comparable composition, but the climates of
the cities should also be very similar.
(c) As the main aim of fluoridation
is to reduce the dental caries attack rates, it is
obviously of importance that the cities to be
compared should have closely comparable dental
caries rates within yearly age groups, of children.
This information can be obtained only by conducting
at least one survey in the cities that are suitable
for comparison on other grounds, so that the fact
that the caries attacks rates are similar is
established prior to the fluoridation of the water
supply of one of them.
Random sampling. The
fundamental importance of random sampling has been
acknowledged for many years. In designing an
experiment, as Quenouille (1952) said, "it is
necessary to allot the treatments to the available
material at random if unbiased estimates of both the
effect of the treatments and also the
reproducibility of the effects are to be obtained."
Therefore, a random device should be employed to
determine which of the participating cities is to be
the test one.
Variation. Fisher (1950)
emphasized this important matter when he said that
"from the modem point of view, the study of the
causes of variation of any variable phenomenon, from
the yield of wheat to the intellect of man, should
be begun by the examination and measurement of the
variation which presents itself." As was pointed out
by Hill et al. in 1950: "It is to be expected
that the rate of caries in all teeth varies from
year to year due to chance." Therefore, a basic
requirement of a fluoridation study is the
assessment of the variability of the caries attack
rates.
Examiner variability. In
experiments in which, of necessity, the subjective
judgment of examiners is employed, an important
consideration is the assessment of
"between-examiner" and "within-examiner"
variability. The former type of variability is
disclosed when different examiners observe the same
subjects, and the latter type is seen in the
different results reported by the same examiner
inspecting the same subjects on different occasions,
but which are sufficiently close together to ensure
that the dental condition has not undergone
appreciable change.
The important effect which examiner
variability can have on the results of a study of
dental caries attack rates was pointed out by
Radusch (1941) and by Dunning (1950). A recent
example is seen in the paper of McCauley and Frazier
(1957). Their Table I shows that in the examinations
made by one examiner in 1955 of Negro boys and girls
who were six years old, in both sexes the DMF rate
per 100 teeth erupted, and also the DMF rate per
child, were found to be about four times as great as
those reported for the same age groups in 1952 when
they were examined by several examiners. The authors
considered that "it is entirely possible that the
1952 findings were influenced by a bias stemming
from subjective differences in the appraisal of
tooth decay by different dentists". Between-examiner
variability of such a magnitude can, of course,
vitiate the results of a study. Unless the examiner
variability is determined, and is taken into
account, the conclusions drawn from a study of
caries attack rates must be treated with reserve.
Examiner bias. In designing
an experiment of this nature, one aim should be to
eliminate examiner bias. This may arise if the
examiners know whether the children they are
examining belong to the test or to the control city.
One method of doing this is to transport to a common
examination centre the small number of children,
some from the test and some from the control city,
that can be examined each day; the examinations
being conducted in a random order which is unknown
to the examiners. It is not suggested that in the
absence of such precautions the examiners exhibited
intentional bias; indeed, as Armitage (1954) pointed
out, "through fear of being biased" the judgment of
an examiner may be influenced.
THE GRAND RAPIDS STUDY
The city selected as the
"fluoride-free" city for comparison with Grand
Rapids was Muskegon, Michigan, "whose source of
drinking water supply and geographical and
climatological characteristics were similar to those
of Grand Rapids" (Dean et al. 1950). This
city was the only control one in which the caries
attack rates in each year were published for each
yearly age group. Unfortunately, its usefulness was
marred by a number of features.
Large differences in sample size.
The reliability of a mean rate is greatly influenced
by the number of observations on which it is based.
Because of the small number of subjects included in
some age groups in some years in Muskegon, little
reliance can be placed on the values stated. In
twelve categories fewer than twenty children were
examined. One "group" consisted of only one child,
whereas one contained 462 children (Arnold et al.,
1953). In the test city the variation in sample size
was even greater, from 18,606 to 3 subjects.
Sampling by school class.
"selected age groups of children are examined within
each of the schools. Selection is made on the basis
of school grade or class, using all children present
in a class or grade of a school." (Arnold et al.
1953). These grades or classes were examined in
1945, an additional grade being examined in 1946,
1947 and 1949, and two more in 1950, making a total
of eight grades in 1950 and 1951. In the last
mentioned year Muskegon ceased to act as a control.
Different methods of sampling.
In Grand Rapids the "annual study sample was
selected after careful review of census data and
consultation with city planning department
officials. On the basis of available information,
the 31 school districts of Grand Rapids were
classified on a socio-economic basis. From the 79
schools in these districts, 25 representative
schools were selected, and the examiners were
assigned schools on a basis of equal sized samples
of comparable population groups" (Arnold, et al.,
1953). However, that strange procedure was not
followed in Muskegon, the same authors stating that
"In Muskegon, the annual examinations have been
conducted in almost all schools, excluding only a
few small schools on the periphery of the city where
many students are from rural areas."
Changes in examiners. In the
report of this study up to and including 1951 (in
July 1951 Muskegon ceased to be a control), it was
stated: "There have been changes in dental examiners
with the exception of one officer who has
participated in each series of examinations. Each
new examiner has been calibrated against this one
officer to standardize diagnostic criteria" (Arnold
et al., 1953). The degree of success of this
odd calibration procedure was not stated.
Examiner variability not assessed.
In 1953 Arnold et al said that "Bite-wing
X-ray examinations were made of a representative
sample of children examined by the different
examiners to evaluate, in part, the "examiner
error"." However, such a procedure cannot replace
the data that could have been obtained by a
correctly designed examination process, which would
have enabled the determination of between-examiner
and within-examiner variability.
Late examination of control city.
The authors of this study did not determine the
caries attack rates in children in Muskegon prior to
accepting this city as a suitable control, for
comparison of two of their statements makes it clear
that the results of the basic examination in the
control city were not known until after the water of
the test city was fluoridated. They stated that
"Fluoridation of the Grand Rapids water supply was
started January 25, 1945" (Dean et al.,
1950), and that the "basic examinations in Muskegon
were not done until late spring of 1945" (Arnold
et al., 1953).
Water of control fluoridated.
Another fact which limits the usefulness of Muskegon
as a control city is that its water supply was
fluoridated in July 1951 (Arnold et al.,
1953), so that the results obtained after that date
had no value as controls for those of Grand Rapids.
This event occurred six and a half years after the
institution of fluoridation in Grand Rapids, and
therefore at a time when, in the latter city, few of
the permanent teeth had erupted in the children that
had been ingesting fluoridated water since birth.
Ignorance of commencement of
fluoridation in control city. The fact that
Muskegon had ceased to be a control by having its
water fluoridated in July 1951 was not always
realized. For instance, Black (1955) in a paper
"Presented before Section on Public Health
Dentistry, ninety-fifth annual session, American
Dental Association, Miami, Fla., November 8, 1954" -
over three years after the institution of
fluoridation in Muskegon (Arnold et al. 1953)
- said that "At Muskegon, Mich, the control city
where fluoride-free water is used, the incidence of
dental caries is unchanged and approximates the
norm." Black was commenting on the findings made
"After eight years of fluoridation at Grand Rapids"
(that is eighteen months after the fluoridation of
the Muskegon water). No information has been found
in the literature with regard to the "national
norm", in fact a feature of these trials has been
the divergent pre-fluoridation rates. The differing
caries attack rates seen in different localities,
even in the same state, were illustrated by Hagan
(1947) and by Hadjimarkos and Storvick (1949, 1950).
A similar statement to that of Black
(1955) was made by Martin (1956) in a lecture
delivered at the fourteenth Congress, Australian
Dental Association, Melbourne, March 1956; that is,
over four and a half years after the Muskegon water
was fluoridated. He said: "The decay rates in the
fluoride free control area (Muskegon) have remained
unchanged." The paragraph containing the
above-mentioned quotation cites as reference Arnold
et al. (1953), who in that paper said: "The
water supply at Muskegon remained unchanged until
July 1951, when the city started adding fluorides to
its water supply."
Variations in Muskegon rates.
Tables 3 and 4 of the report of the seventh year
of the Grand Rapids study (Arnold et al.,
1953) show that both the def (decayed, extraction
indicated, or filled deciduous teeth) and the DMF
rates reported from Muskegon from year to year
differed considerably from those of the first
examination. Despite this fact, the statement that
the incidence of dental caries in Muskegon was
unchanged was made by Black (1955) and Martin
(1956), amongst others. These statements are at
variance with that of the authors of the study
(Arnold et al., 1953), for they mentioned the
changes in these words: "A similar comparison of
results at Muskegon shows the percentage reduction
to range from 1.5 percent in 6-year olds to a high
of 15.5 percent in the 11 year olds" in the
permanent teeth.
The magnitude of the changes.
The statement which has been quoted above does not
reveal the magnitude of the changes which were
observed in the DMF rates in the control city. The
percentage reductions given were obtained by the
method commonly used in all these studies, that is,
the difference between the most recent and the
original DMF rate was expressed as a percentage of
the original rate, the variations obtained in the
intervening years being ignored. The changes which
occurred would have been more obvious if, for
instance, the results for Muskegon had been computed
in 1946 instead of in 1951. In that case the
"reduction" would have been 40.7 per cent instead of
1.5 per cent in the six-year old, and 32.7 per cent
instead of 15.5 per cent in the eleven-year-old
children.
Sampling error. Arnold et
al. (1953) stated that the percentage reductions
obtained in Muskegon "may, in part, represent
sampling error." It was not conceded that such an
error could also apply to the results from the test
city, nor were suggestions made as to the cause of
the remainder of the reductions in the control city.
These cannot be attributed to changes in the water
supply, for they stated: "The water supply at
Muskegon remained unchanged until July 1951, when
this city started adding fluorides to its water
supply" (Arnold et al., 1953).
Variation in Muskegon. The
variability from year to year in the mean rates
reported from Muskegon, which, it will be recalled,
were stated to have remained unchanged (Black, 1955;
Martin, 1956) are illustrated in Figs. 1 and 2. The
data from which these figures were drawn are from
Tables 2 and 3 (with errata corrected) of Arnold,
Dean, Jay and Knutson (1956). The point shown in
Fig. 2 for the sixteen year-old children in 1946
should be disregarded, as this age "group" consisted
of only one child.
Comparison of the series of baseline
rates for DMF in Grand Rapids and in Muskegon does
not reveal that one series was consistently higher
than the other. However, with the exception of the
eleven and twelve-year old children, the def rates
in Muskegon were higher than they were in the test
city.
Comparison with Aurora.
Arnold et al. (1953) said: "To establish what
might be termed an "expectancy curve" for this
study, a natural fluoride area, the city of Aurora,
Ill., was selected. The Aurora water supply contains
1.2 ppm F and has a reliable "history of constancy
back to 1895." It was not stated whether factors
other than the fluoride content of the water supply
were considered in selecting this city. The fact
that other influences can be of importance was shown
in the recent study by Russell (1956) in
Montgomery-Prince Georges counties. Prior to the
institution of fluoridation, in the total sample of
subjects the def rates for children whose mean ages
were 5.44, 6.47, 7.45 and 8.49 years were lower than
those of children of similar ages in Aurora.
Limitations of Aurora data.
The caries attack rates reported from Aurora
consist of a single series obtained by several
examiners in 1945-6. Therefore, there is no
information with regard to variations from year to
year in the mean value of the rates, and examiner
variability was not considered.
MUSKEGON
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THE GRAND RAPIDS STUDY
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Figure 1.
The mean number
of def deciduous teeth per child in Muskegon,
Michigan, the "fluoride-free" control city for
Grand Rapids, Michigan, at each year of
examination. The 1945 examination was made in
the "late spring", those of the other years, in
October and November. Data from Table 2, Arnold
et al., 1956. Three months prior to the
1951 examination the water of this city was
fluoridated. It has been stated (see p. 145 -
146) that these rates "remained unchanged"
during the period shown.
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Figure 2.
The mean number
of DMF permanent teeth per child in Muskegon,
Michigan, the "fluoride-free" control city, at
each year of examination. Data from Table 3,
Arnold, et al., 1956. It has been stated
(see p. 145 - 146) that these rates "remained
unchanged" during the period shown.
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