https://www.blogger.com/nullCh. 3 The Greatest Fraud
Fluoridation:Errors and Omissions in Experimental Trials - 1c THE BRANTFORD
STUDIES by Philip R.N. Sutton from fluoridationfacts.com
Errors and Omissions in
Experimental Trials - 1c
THE BRANTFORD STUDIES
In the
city of Brantford; Canada, two independent trials were conducted.
1. The City Health Department
Study
In this
study no control procedure was attempted. However, it will be considered
briefly because two pre-fluoridation surveys were made by the school dental
officer and his assistant (Hutton et al.,
1954). This is the only one of these five trials in which more than one
pre-fluoridation survey was made in the test city; and, with the exception of
Muskegon, none of the control cities provided data obtained in successive years
from individual yearly age groups.
Were results combined or averaged? Hutton et al. (1951) stated that "The results of these two
[pre-fluoridation] surveys have been combined and are shown in Table I."
In Tables I and II of the Ontario Department of Health Report (1956) the rates
for those two surveys were shown separately. With the exception of those of the
nine-year-old children, for both the deciduous and the permanent teeth, the
mean of the two rates for each age is identical (to one decimal place) with the
mean rate computed from the figures of the combined survey which were supplied
by the authors (Hutton et al., 1951,
Table I). This result could have arisen only if (with the
exception of the children who were nine years old) the number of
children of the same age examined on both occasions was equal, or almost
exactly so - a most unlikely event; or if the results were not combined, as
stated by the authors, but the rates obtained in 1944 and 1945 were averaged.
The United Kingdom Mission (1953) stated that "the average figures of
these two years" were used. If the rates for the two years were averaged,
there were errors in computing the rates of the nine-year-old children, or
errata in one or more of those three tables. The figures shown in Tables I and
II of the Ontario Department of Health Report (1956) should be treated with
caution, because in both of these the year of fluoridation is stated
incorrectly, and in the former table the "% Reduction Since 1944-45"
for age seven years should be 66, not 51; whereas in the latter one, the
"% Reduction Since 1948" for age nine to eleven years in Stratford
and Sarnia should not have been indicated by dashes, but by five and sixteen
respectively.
2. The National Health and Welfare
Study
The other
study in Brantford was conducted by the Canadian Department of National Health
and Welfare, and was described by the New Zealand Commission of Inquiry (1957)
as "the most complete of the 10-year North American studies".
Late commencement. Unfortunately, this trial was not
begun until January 1948, over two and a half years after the commencement of
fluoridation of the Brantford water supply (Brown, 1951). Such delay must
affect the value of this study, unless it is assumed that the structural theory
of reduction of dental caries as a result of the ingestion of fluorides is
correct, and that this is the only way in which fluorides may affect the
incidence of caries. This theory was advanced by Cox and Levin in 1942, and was
widely accepted at the time these trials were initiated (Dean et al., 1950; Ast et al., 1950). If this theory is correct (as was noted in Part
One), little change can be expected in the DMF rates until about six years
after the commencement of the study. It is evident that this theory must still
be held to be correct in some quarters, for the recent report of a dental
caries survey conducted by McCauley and Frazier (1957) stated: "Although
fluoridation of the Baltimore City water supply was begun Nov. 26, 1952, (27
months before the survey), there was no reason to anticipate substantial change
in the caries experience of these children in this relatively short period of
time." However, even before the commencement of the Department of National
Health and Welfare study in Brantford, the City Health Department examiner's
figures for 1947 showed great reductions in the DMF rates since the
introduction of fluoridation. This result was not published by Hutton et al. until 1951, but must have been
available to the investigators who "came to the scientific rescue of the
project early in 1948" (Hutton et al.,
1956). Indeed, in his first report, Brown (195 1) acknowledged the help and
advice of two of the three authors of the City Health Department Report (Hutton
et al., 1951).
The control cities. The
city of Sarnia was chosen as the "fluoride-free" control, and
Stratford as the control city with a water supply which "contains 1.3 ppm.
of fluorine from a natural source" (Brown, 1951). The reasons for the
selection of these cities were not given, except that it was said: "sarnia
and Stratford, two cities in Western Ontario known to be comparable to
Brantford, except for the fluoride content of their water supplies, agreed to
serve as controls" (Brown et at.\,1954b). Also, Brown, Josie and Stewart
(1953) said that Sarnia was "a city" which has fluoride-free water
and is sufficiently similar in size, location, and other attributes for
purposes of the comparison". The United Kingdom Mission (1953) stated:
"Before this study was undertaken the socio-economic status of the three communities
was examined and found to be reasonably comparable."
Superior dental care in Brantford. The United Kingdom Mission (1953)
said: "Brantford, however, over a period of 15 years, has provided more
free dental services for children than most Canadian cities, and this has
resulted in the ratio of corrected to total defects being higher than in either
Sarnia or Stratford." It considered that in Brantford "dental care
was outstandingly good." Also, Brown, in 1952, said:
"the
recordings so far obtained indicate both a higher treatment 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 pre-fluoridation survey on a
comparable basis is a further limiting factor in interpreting the
results."
No pre-fluoridation survey. The
authors of this Brantford study (Brown et
al., 1953) said:
"As
the study does not include a pre-fluoridation survey, the full amount of
benefit which the Brantford teeth have received since fluoridation cannot be
illustrated directly from the data for Brantford. Some idea of the extent of
the benefit can be obtained by comparison with the data for Sarnia.... By 1948
the Brantford data were not greatly different from those for Sarnia."
This
remark suggests that the data for the two cities prior to fluoridation in
Brantford were similar, and that this process had had little effect on the
caries rates up to the time of the 1948 examination in Brantford.
Doubtful comparability of rates. Owing to the delay in setting up
this study, it cannot be established how closely the dental caries attack rates
in Brantford resembled those in Sarnia, at the time fluoridation was instituted
in the former city. There is evidence that the dental condition of the children
in those two cities was not closely comparable, for Brown et al. (1953) stated that "even by the time of the first
survey, mean tooth mortality in Brantford was much lower than in Sarnia, for
all age groups."
This
comment implies that, even by the time of the first survey, as a result of
fluoridation the tooth mortality in Brantford had decreased considerably. This
concept is not consistent with the one mentioned in the last paragraph. At the
time of the first examinations, the tooth mortality in the six to eight years
age group was more than four times as great in Sarnia as it was in Brantford,
and in each of the other two age groups it was almost twice as great (Brown et al., 1953, Table 3.)
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Figure 6. The
gross differences observed in the tooth mortality (teeth which are missing or
which must be extracted) in Brantford and its control city of Sarnia, during
the initial examinations. Canadian Department of Health and Welfare study.
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The influence of treatment. The fact that such large differences
were reported in tooth mortality rates in the two cities even in the older age
groups suggests that dental treatment in them was different, and the authors
stated that "Both preventive and treatment measures may have a decided
effect on tooth mortality rates" (Brown et al., 1953). It may be recalled that the United Kingdom Mission
(1953) noted that Brantford was unusually well provided with free dental
services "and this has resulted in the ratio of corrected to total defects
being higher than in either Sarnia or Stratford."
Tooth mortality. Brown et al. (1953) said that "there has been a decrease in tooth
mortality in Brantford between successive surveys"; but, in fact, the 1953
rate (Table 3) in the children aged six to eight years was the highest up to
that time. This statement was corrected in the next report (Brown et al., 1954b) by prefixing "in
almost all cases" to the previous statement. In this connection, the
authors remarked in 1953 that, "as well as the fluoridation of the
Brantford-water supply, other factors such as differences in preventive or
treatment measures are probably affecting the Brantford position." There
appears to be no reason why those of the control cities should not have been
similarly affected.
Differences in oral hygiene. Additional evidence which suggests
that a difference existed between the dental condition of the children in
Brantford and that of children in the control cities is provided by the data
with regard to oral hygiene. Brown et al.
(1954b) stated:
"Classification
and recording of oral hygiene was undertaken because it was considered that
marked differences in oral hygiene as between the test and control groups might
conceivably affect the findings--or at least might be taken into consideration
as a modifying factor, although not a strictly measurable one. However, the
figures here suggest that, since 1948, differences in oral hygiene status could
not have been a major factor in either the caries level changes within
Brantford or the caries level differences between the control cities."
As no
comparisons were made between the control cities, the last phrase of the
quotation is thought to refer to the caries level differences between Brantford
and each of the control cities. The authors' Table 11 indicates that, in the
first examinations, in the test city the percentage of subjects who had a good
oral hygiene status was almost twice as great as that present in children in
both the control ones; these were, Brantford 34.3 per cent, Sarnia 19.7 per
cent and Stratford 17.8 per cent. Considerable differences between the oral
hygiene status of the children in the test and the control cities were also
recorded during the later examinations. These were clearly "marked
differences" though the authors did not consider them important.
The concentration of fluorides. Brown et al. (1954b) stated:
"The
Brantford Fluoridation Caries Study was undertaken with a view to finding out
whether or not the raising of the fluoride content of a previously
fluoride-free water supply to 1 part per million, by the mechanical addition of
sodium fluoride, would reduce the incidence of dental caries to that which
obtains where water supplies derive about 1 part per million of fluoride from
deposits in the earth."
A
fundamental requirement of a test of this nature is that the water supply of
the control city should contain the same concentration of fluorides as that of
the test one, but Brown, McLaren, Josie and Stewart (1956) reported: "The
Stratford water supply contains a concentration of fluoride which is 60% higher
than that used in Brantford."
Differences of opinion. Several different statements were
made regarding the concentrations of fluorides which were present in the water
supplies of Brantford and Stratford.
1. Brantford. The New Zealand Commission of
Inquiry (1957) said that the water supply of Brantford was "raised to 1.2
ppm. in 1945". The authors of the City Health Department study (Hutton et al., 1951) stated that in February
1949, "the dosage was raised to produce 1.20 ppm."; but in 1954 they
stated that "The fluoride content of the finished water is maintained at 1
ppm." In reporting the National Health and Welfare Study, Brown (1952)
stated that "a fluorine concentration of between 1.0 and 1.2 ppm. has been
maintained in the water supply continuously" since June 1945; and in 1956
Brown et al. said: "Brantford
has had more than 10 years of experience with 1 part per million fluoride in
its water supply." These statements that the fluoride content was
"maintained" at "1 ppm" and "between 1.0 and 1.2
ppm" should be considered in conjunction with that of the United Kingdom
Mission (1953): "For example, in 1951 the average for the year was 1.2 ppm
with a variation between 0.75 and 1.45 ppm., however, the figures below 1.1 ppm
and above 1. 3 ppm were few in number."
2. Stratford. The supply of Stratford was
stated to have 1.2 ppm of natural fluoride in its domestic water (Ontario
Department of Health, 1956; New Zealand Commission of Inquiry, 1957). However,
in reporting the National Health and Welfare study in 1951 and 1952, Brown
stated that it "contains 1.3 ppm. of fluorine"; and, with his
co-workers, the following year said that "in Stratford where the water
supply, obtained from deep wells, has contained 1.3 ppm." (fluoride)
"from natural deposits continuously since 1917" (Brown et al., 1953). In their next report
dealing with dental caries (Brown et al.,
1954b), the figure stated was "1.3 to 1.6 parts per million of
fluoride"; but in the following report these authors (Brown et al., 1956) said that this water
supply "contained 1.6 parts per million of fluoride since 1917", and
also that 1.6 ppm fluoride content "has been in continuous use for thirt
yeight years."
These
different statements, although strange, may be considered to be unimportant
from the practical point of view, but very small changes in the fluoride
content of the water may have considerable effects, as reports by Deatherage
(1942) and Galagan and Lamson (1953) indicated. The latter authors found that
"In water supplies of the Arizona communities studied, concentrations of
fluoride above 0.8 ppm resulted in objectionable dental fluorosis;
concentrations of 0.6 to 0.8 ppm resulted in an occasional diagnosis of
fluorosis; concentrations below 0.6 ppm did not cause objectionable
fluorosis." The mean temperatures of these communities were between 67 and
72 degrees Fahrenheit.
Three misleading statements. In the summary of the 1954b
report of the National Health and Welfare study, Brown et al. stated that during the period 1948-54 "dental caries
experience of children in the two control cities, on the other hand, either has
remained at about the 1948 levels, or has increased slightly, at all ages
studied." A similar statement was made by them in the 1955 Report (Brown et al., 1956): "During that time
[more than ten years] a very important, statistically significant reduction in
tooth decay has occurred in all the age groups studied, while in the two
control cities of Sarnia and Stratford it has either remained at about the same
level or increased somewhat." The last sentence contains three misleading
statements about the control cities:
(a) As
this study did not commence until 1948 with "examinations in Sarnia
beginning in March of that year, and in Stratford in October" (Brown,
1952), and as fluoridation in Brantford commenced in June 1945 (Hutton et al., 195 1), no information is
available with regard to the prevalence of "tooth decay" in Sarnia
during the first two and three-quarter years, or in Stratford for the first three
and a quarter years of the ten-year period of fluoridation which these authors
were discussing in their 1955 Report. Therefore, it cannot be known whether
this condition "remained at about the same level" in the control
cities during the early years of fluoridation in Brantford.
(b) No
remarks were made in the context of this statement in this (or the previous)
paper which suggested that reference was being made to the permanent teeth
only, but these statements are not correct for the deciduous teeth. (However,
in the former paper, a similar statement to that made in the summary was also
made under the heading "Mean DMF Permanent Teeth".) Decreases in the
df (decayed, filled deciduous teeth) rate were seen in the nine to eleven years
group in both Sarnia and Stratford, that in the former city being shown by
these authors to be statistically significant (Brown et al., 1954b, Table 10).
(c) In
both cities the mean rates of DMF and df teeth per child showed changes which
were said to be statistically significant (Brown et al., 1954b).
Omission of decreases. The decreases in the caries
attack rates of the deciduous teeth, which have been mentioned above, were also
omitted in Table II of the Report to the Minister of Health, Province of
Ontario, Canada, by the Division of Medical Statistics, Ontario Department of
Health, which was made in 1955 (Ontario Department of Health, 1956). Under the
heading "% Reduction Since 1948", these decreases were not shown, but
instead, in the appropriate positions dashes were printed, despite the fact
that in Sarnia the percentage reduction (determined by the method commonly used
in these studies) was 16 per cent, almost as great as that of 18 per cent shown
for the same age group in the test city; furthermore, this reduction in Sarnia
was stated by the authors (Brown et al.,
1954b) to be statistically significant.
Different rates reported. It should be noted that the
deficiency in the data of the National Health and Welfare study, owing to its
late commencement, could not be decreased by comparing the rates obtained by
its examiners with those reported by the City Health Department examiner,
because of the considerably lower rates recorded by the last-mentioned examiner
when impecting similar groups of children. For instance, in their examination
in 1948, for children aged six to eight, nine to eleven and twelve to fourteen
years, Brown et al. (1953) obtained
rates of 1.41, 4.07 and 7.68 respectively for the permanent teeth, compared
with rates of 0.84, 3.37 and 6.11, for the same age groups of children, in the
same city and in the same year, obtained by the City Health Department examiner
(calculated from Table IV, Hutton et al.,
1951).
Significant fluctuations in
controls. In the
two control cities "where it is presumed that there has been no
appreciable change in either preventive or treatment services" (United
Kingdom Mission Report; 1953), it can be seen in Tables 4, 6, 8 and 10
published by Brown et al. (1954b)
that some considerable fluctuations in the caries attack rates were recorded;
more than half of the inter-year differences in each of the control cities
being shown to be statistically significant. However, in the text it was stated
that the "dental caries experience of children in the two control cities .
. . either has remained at about the 1948 levels, or has increased slightly, at
all ages studied."
(1)
Sarnia. In this city the changes between examinations of the rates for the
deciduous teeth were not very marked, but there was a significant one between
1948 and 1954 in the nine to eleven years age group. However, in the DMF
permanent teeth, there were four definitely significant (three standard error
level) and one significant change in the nine comparisons made. In regard to
the first permanent molars, there were six significant (including three
definitely significant) alterations in the rates, in the nine comparisons made
(Brown et al., 1954b).
(2)
Stratford. In this city, the rate of df teeth per child showed a significant
difference in one case out of the four comparisons made between successive
examinations (Brown et al., 1954b).
In the DMF permanent teeth per child, the results of the four examinations
were: 0.41, 0.75, 0.47 and 0.67 for the six to eight years group; 1.13, 1.76,
1.46 and 1.89 for the nine to eleven years age group; 2.55, 3.12, 3.02 and 3.77
for the twelve to fourteen years age group (Brown et al., 1954b, 1956). These variations between examinations were so
large that five out of the six comparisons made (in the 1954b report) between
successive examinations were said to be statistically significant, four of them
being at the three standard error level. In the last report published (1956),
Brown et al. abandoned the method
which they had used in the two previous ones, that of showing the standard
error of the mean values of the DMF rates, and of making "Inter-City"
and "Inter-Year" comparisons (Brown et al., 1953, 1954b). Therefore it was not stated whether the
differences between the 1954 and the 1955 DMF rates in Stratford were
significant, but it can be seen that they were marked; the difference of 0.75
in the twelve to fourteen years group being considerably larger than any of
those stated in the 1954b report to be significant differences between various
examinations in that city. When the DMF rates for the first permanent molars
are considered, similar marked changes are seen, and in five of the six
comparisons the differences were significant (four definitely so).
Larger "percentage"
changes in a control.
If one resorts to the method commonly used in these trials - that of expressing
the alteration in the DMF rate as a percentage of the original rate - these
unexplained increases in the control city of Stratford between 1948 and 1955,
although they were described as "no change" (Ontario Department of
Health, 1956), and as "a slightly higher prevalence of dental caries in
1955, over the 1948 levels" (Brown et
al., 1956), are found to be 63 per cent, 67 per cent and 48 per cent, for
the six to eight, nine to eleven and twelve to fourteen years age groups
respectively. In each case these percentage changes are considerably larger
than those of 51 per cent, 44 per cent and 37 per cent which can be computed
from the data reported for Brantford. The last-mentioned changes were
attributed to fluoridation, and each was stated to indicate "a very
important, statistically significant reduction in tooth decay" (Brown et al., 1956).
This is
just one instance of the strange results which are obtained when this method of
calculation is used. It should be realized that it was the one most commonly
employed in fluoridation trials, and was used in formulating the
often-expressed claim that (as stated by Arnold et al., 1956): "In children born since fluoridation was put
into effect, the caries rate for the permanent teeth was reduced on the average
by about 60 per cent." The recent World Health Organization Press Release
(WHO/45, 4 September 1957) stated - with no mention of age - "The
prevalence of dental caries in the permanent teeth of children decreased some
60 percent".
A smaller "percentage
decrease" after long fluoridation. The "percentage decreases" which have just been
mentioned (51 per cent, 44 per cent and 37 per cent, calculated by the method
described in the last paragraph) were not stated in the 1956 report of Brown et al., but the figure of 51 per cent
for the six to eight years age group is considerably less impressive than the
figure of "approximately 69%" published in the 1954b report from this
study. Although the final report (1956) gave the rates for 1948 and 1955 only,
and therefore did not show the fluctuations between examinations, from the
1954b and 1956 reports of Brown et al.
it is seen that the marked change in the "percentage" decrease which
has just been mentioned was due to the DMF rate in Brantford in 1955, for this
age group, being the highest seen since 1951. Ignoring the fact that in
"children born subsequent to fluoridation" the "decrease"
in the DMF rate had dropped to only 51 per cent, the authors stated in the
final sentence of their final report (1956): "For every three decayed
teeth they would have had, they have only one."
More misleading comments. Turning from the reports made by
the authors of this study about the control cities to some of the comments made
by others, it is seen that these are even more misleading. Only two will be
mentioned. Martin (1956) stated that during "the 1948-54 period" the
"DMF figures for the two control areas have remained at 1948 levels."
The authors of the Ontario Department of Health Report (1956) went so far as to
state to their Minister of Health that "it had been established that there
has been no change in the already low dental caries attack rates in Stratford
... or in the relatively high rates for Sarnia".
These two
statements are contrary to the results published by the authors of the study
(Brown et al., 1954b), which showed
that in both the control cities there were statistically significant
differences between the caries attack rates at successive examinations. Out of
the fifteen comparisons made, only five differences in the rates were not
significant, two changes were significant and eight changes were definitely
significant.
Unexplained significant changes in
controls. All the
changes in the caries attack rates in the control cities which were reported to
be significant are unlikely to be chance variations; therefore, to what factor
or factors must they be attributed. It is possible that they were due, in whole
or in part, to alterations in the "weighting", such as were found in
the Evanston study as a result of combining the caries attack rates of children
of different ages (Hill et al.,
1952). However, as the age composition of the groups was not stated in this
study, it cannot be determined to what degree the data was distorted by "weighting",
a condition which is almost inevitably present when data drawn from several
different yearly age groups are combined.
Apart
from deficiencies which are found in other studies also, in this trial there is
an absence of any information regarding the caries attack rates in Brantford
and Sarnia, prior to the fluoridation of the water supply of the former city.
There is also the fact that no explanation was given by the authors for the
significant variations in the caries rates in the control areas. Therefore, a
marked decrease in dental caries in the test city as a result of fluoridation
cannot be said to have been established.
THE NEWBURGH STUDY
The
fluoridation trial conducted in Newburgh differs from the other studies in two
important ways:
1. In
almost all the comparisons made, the data obtained were compared with those
from Kingston, the "fluoride-free" control city, instead of the
method used in the other trials, by which most comparisons were made between
the initial and the latest observations in the test city.
2. The
caries attack rates were stated per 100 erupted teeth, instead of per 100
children or per child. The Evanston study was the only other one in which the
caries rate per 100 erupted teeth was published; Hill et al. in 1955 and 1957a showed this rate, but only for children
aged twelve to fourteen years.
The control city. Kingston
was used as the control area. "Both cities are situated on the Hudson
River about 30 miles apart. Each has a population of approximately 30,000. The
climate of both cities is also similar, and their water supplies at the outset
of this study were comparable and have remained so, except for the addition of
sodium fluoride to Newburgh's supply" (Ast et al., 1950). Ast and Chase (1953) added the information that the
two cities had a "comparable age, sex, and color distribution"; and
Schlesinger, Overton and Chase (1950) mentioned that they "bore a close
resemblance to each other in respect to size and socio-economic
conditions".
Late examination of control city. In Kingston, as in the other
"fluoridefree" control cities that have been considered, the basic
examinations were not made until after the fluoridation of the water supply of
the test city. Fluoridation was started in Newburgh on 2 May 1945 (Ast et al., 1950), but the examinations in
Kingston were not conducted until "Sept., 1945 - Feb., 1946" (Ast et al, 1950).
Considerably different composition
of waters. In
1950 Ast et al., stated that the
water supplies of Newburgh and Kingston "at the outset of this study were
comparable and have remained so, except for the addition of sodium fluoride to
Newburgh's supply." However, both the source and the composition of the
water supplies of these two cities are different. The United Kingdom Mission
(1953) stated that the source of Newburgh's water is from "surface water.
Algae growths in spring and summer checked by copper sulphate blown on the
surface of the water as a powder." The source of Kingston's supply was
described as "Mountain spring impounded. Auxiliary supply, small spring
reservoir" (Lohr and Love, 1954).
In regard
to the composition and other characteristics of these waters, according to
analyses of the finished waters made in February 1952 by the U.S. Geological
Survey (Lohr and Love, 1954), in each of the ten items - magnesium, sodium,
potassium, bicarbonate, sulphate, chloride, dissolved solids, specific
conductance, hardness and alkalinity - the values for the Newburgh water were
at least four times as great as those obtained from analysis of the Kingston
supply. In the very important matter of the calcium content, the Newburgh value
of 35 ppm (Ca) was more than five times as large as that of the Kingston one of
6.6 ppm (Ca). Changes in the supplies during the period of the trial, owing to
natural or to treatment-chemical variations, are unlikely to have affected
these gross differences more than slightly.
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Figure 7. The
considerably different calcium and magnesium content and hardness of the
water supplies of Newburgh and its control city of Kingston, February 1952.
Eight other characteristics of the Newburgh water were at least four times as
large as they were in Kingston. The authors of this study stated that these
waters "at the outset of this study were comparable and have remained
so" (Ast et al., 1950).
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An unsatisfactory control. In proposing this study, Ast
(1943) said: "Much care must be exercised in the selection of study areas
which should be comparable in as many essential factors as possible." The
first of these factors which he mentioned was the "chemical composition of
past and present water supply". Therefore it is surprising that Kingston
was selected as the control city for Newburgh, for it is clear that in this
very important matter the two cities showed considerably different values. The
importance of the close comparability of the water supplies was emphasized by
the statement of the American Water Works Association (1949) 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."
Variations in methods used. An
outstanding characteristic of this study is the variation in the methods used,
both in gathering the data and in the presentation of the results. There were
changes in the examiners; on some occasions clinical examinations only were
made and on others X-rays were also used. The statisticians changed, as did
their presentation of the data in age groups. The sampling method varied in
regard to residence qualifications, and changes occurred in the age range of
the children who were examined. In one report data was obtained from selected
schools only. In some examinations the sampling method was different in the
control city from that used in the test one, All these matters will now be
considered more fully.
The dental findings. These were published in five
papers. Ast, Smith, Wachs and Cantwell, in 1956, said: "Progress reports
were published after three, four, six and eight years of fluoride experience in
Newburgh" (Ast et al., 1950,
1951; Ast and Chase, 1953; Ast et al.,
1955). The last-mentioned report (Ast et
al., 1955) "after eight years of fluoride experience" gave the
results obtained during the examinations of 1953-4. The final report, giving
the results for 1954-5, apparently one year later than those in the fourth
dental report, was said to show the "dental findings after ten years of
fluoride experience" (Ast et al.,
1956). However, as fluoridation in Newburgh commenced on "May 2,
1945", and as the examinations given in the final report were made
"between October 1954 and June 1955" (Ast et al., 1956), it would appear that, at the most, only a small part
of the data of the final examination was obtained "after ten years of
fluoride experience."
Different examiners used. The initial examinations in both
cities were made by Finn. "The subsequent examinations in Kingston using
the same technic were made by two dental hygienists" (Ast et al., 1950). The examinations in
1951-2 were conducted by two examiners, but "Due to loss of one of the
examiners during the examination year, it was deemed advisable to use only
those examinations made by the remaining examiner in both cities" (Ast and
Chase, 1953). The clinical examinations in 1953-4, and the final ones, were
made by Wachs (Ast et al., 1955,
1956). These changes were made despite the fact that in 1943 Ast said that
"the examinations throughout the study should be made by the same dentist
because of the marked variation in diagnosis of small carious lesions, pits,
and fissures by different dentists."
The
clinical examinations were supplemented by the use of X-rays in the years
1949-50, 1953-4 and 1954-5 (Ast et al.,
1956). In the first of these, which was confined to children aged seven, nine
and eleven years, the X-rays were taken by a staff dentist and were read by Ast
and Finn (Ast et al., 1951). The next
series was taken by Wachs and was read by Bushel (Ast et al., 1955); the final X-rays were taken by Wachs and a staff
hygienist, and they were read by Wachs and Smith (Ast et al., 1956).
Non-comparability of data. In the last two reports (Ast et al., 1955, 1956), the carious
cavities that were detected by the X-ray were added to those found in the
clinical examinations. Ast et al. in
1955 said that "the data in this report cannot be compared directly to
those earlier data based on clinical examinations alone." However, in
Table 3 of the 1956 report, the results of the clinical examination are shown
separately, but a satisfactory comparison with those obtained in the earlier years
is prevented by the fact that in this report the data were not published for
yearly age groups, but for the age ranges six to nine and ten to twelve years.
Data for the other two age groups which were shown in the final report,
thirteen to fourteen and sixteen years, were not published in the previous
ones.
The rates
for the deciduous teeth were given in only one report (Ast et al., 1951).
Examiner variability. The between and within-examiner
variability was not investigated, although, early in the study, the importance
of this matter was recognized by Ast et
al. (1950) when they stated: "We cannot entirely rule out the
possibility of variation in the interpretations of the examiners. The fact that
more than one examiner was used might alter the differences between Newburgh
and Kingston to some extent." In the following year (Ast et al., 1951) it was stated: "In
the present report an attempt is made to demonstrate that through an objective
roentgenographic examination of the teeth of selected age groups, the question
of examiner bias in this study is not likely to account for the differences
noted." However, the only data published were those of the first permanent
molars; and the finding that "the DMF roentgenographic findings of the
first permanent molars only" in selected age groups shows "consistent
differences at each age in favor of Newburgh" does not provide an estimate
of examiner variability such as could have been obtained readily by normal
statistical methods.
In
addition to the changes in the examiners and in the examination methods, there
were changes in the statisticians. The report after three years of fluoridation
was made in collaboration with one statistician; those after four, six and
eight years with a different one; and a third statistician was employed in the
preparation of the final report.
Different adjustment procedures. In most of the tables in this
study a "Crude rate" and an "Adjusted rate" are shown. The
incongruity of making these small adjustments to rates that were obtained by combining
data from children of considerably different ages does not appear to have been
realized. In some cases even data from children aged between six and twelve
years were added (Ast et al., 1950,
1951; Ast and Chase, 1953), the great increase in the caries attack rate
between those ages being ignored. The adjustments were made (depending on the
type of data) to the tooth population, the first permanent molar population, or
the distribution of children. In the first three reports of dental findings (Ast
et al., 1950, 1951; Ast and Chase,
1953), they were all made to the appropriate situation in Kingston during the
1955-6 examinations, but the adjustment system was then changed, the crude
rates after eight years of fluoridation being adjusted to the situation in
Kingston in 1953-4 (Ast et al.,
1955), and those shown in the final report to that present in the control city
in 1954-5 (Ast et al., 1956).
Variations in age groups. In discussing the Evanston study,
it has already been pointed out that the method of combining the results of
different age groups may result in "weighting" the data, so that
comparisons between the test and the control cities may be affected. In the
examples given >from other fluoridation trials in which this method was
used, the age groups were consistent from examination to examination; but in
the Newburgh-Kingston study the groups varied between examinations, between
comparisons made from data obtained during the same examinations, and even the
age range of the subjects inspected varied from time to time. In regard to the
DMF rate per 100 erupted permanent teeth, the groups were as follows: 6-7,
8-9,10-12 (Ast et al. 1950); 6, 7, 8,
9, 10, 11 and 12 (Ast et al., 195 1;
Ast and Chase, 1953); 6, 7, 8, 9 and 10 (Ast et al., 1955); and 6-9, 10-12, 13-14 and 16 years (Ast et al., 1956).
Changes
in the age groups were also made in reporting the other data presented in this
study, but in many cases the groups were different from those which have just
been mentioned.
Grouping of data hinders comparisons. In the final report, Ast et al. (1956) said: "The data are
combined for six to nine year old children because these children in Newburgh
had used fluoridated water throughout their lives"; and the age groups ten
to twelve years and thirteen to fourteen years were associated with the tooth
calcification pattern. No explanation has been found for the grouping used by
Ast et al. in 1950, but this matter
will be considered later.
Whatever
may have been the reason for adding the data of children of different ages, it
has the unfortunate result of making it very difficult to compare the rates
which were present in the test (and in the control) city at different stages of
the trial, especially as, in the 1955 report of Ast et al., the rates obtained from the clinical examinations were not
shown separately from those computed from the combined clinical and X-ray
results.
"Weighting". Even if the explanation advanced
by the authors of this study is considered to be a reasonable one, there
remains the danger of "weighting" the data by combining into one
category such divergent material as is provided by children of different yearly
ages. One of the tables in which obvious "weighting" is seen is Table
I of the first report (Ast et al.,
1950), "weighting" being present in several different forms. In the
control city, the total DMF rate per 100 teeth (ages six to twelve years) is
"weighted"; for the total number of teeth examined is made up (in
1945-6) of only 11 per cent from the six to seven years age group, with its
comparatively low DMF rate, and of 67 per cent from the ten to twelve years
group with its comparatively high rate (22 per cent was from age eight to nine
years). In the latest examination shown in that table (1947-8), the two
percentages were 17 and 59 respectively, so that the comparison between the
results of the two examinations is also "weighted". Similar instances
of "weighting" are also seen in the data >from the test city; but
as these are of a different degree, the comparison between Newburgh and
Kingston is another instance of "weighting" (Table 1, Ast et al., 1951). It can be seen that some
"weighting" occurred within the age groups used in the baseline
examinations, principally in the eight to nine years group in both cities.
Fewer erupted teeth than expected. In the final report (Ast et al., 1956), from Table I it can be
calculated that the number of erupted permanent teeth in the six to nine years
group in Newburgh was less than the number expected, on the assumption that the
mean age of eruption of each type of tooth was the same as in the children in
Kingston. Also, in the ten to twelve years group (by assuming that in these
children at least the eight incisors and the four first molars would have
erupted) the number of erupted permanent canines, bicuspids and second molars
was fewer in Newburgh than would be expected. Statistically speaking, both
these differences are highly significant.
... Continued on next page.
Cover | Introduction | 1a
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