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SCIENCE SECTION

Sutton 8.2

CRITICISMS AND COMMENTS (Continued)


DR R. M. GRAINGER

The third review of this book in the Australian Dental Journal, by DR R. M. GRAINGER, Division of Dental Research, Faculty of Dentistry University of Toronto, was as follows:

Those whose work has been so unfairly criticized might well ask P. R. N. Sutton if he feels his own work is proof that the unimpeachable study can be done(26), or if he would welcome similar scrutiny of his publications.

While we do not claim to be able to answer every question to P R. N. Sutton's satisfaction (or even our own), in order to help set the record as straight as possible(27) the following are specific comments on points raised by P. R. N. Sutton in his discussion of the Brantford Study. No attempt is made to rationalize why specific workers directed or restricted their research efforts or discussion in any areas other than to comment that they no doubt accomplished as much as they could under the circumstances in which they had to work.

Item 1: Reference to Hutton et al. (1951). The numbers of children of the same age examined in the years 1944 and 1945 were very similar with the exception of the nine-year age group. From the unpublished data released at annual meetings in Brantford the number of children examined in 1944 was 239, and in 1945, 319; making a total of 558 (not 608). The data in Table I (Hutton et al.) were apparently combined by pooling the two years' results not by averaging the averages. However, the point is rather academic(28).

Item 2: Reference to Ontario Health Department report. The date of water-fluoridation in Tables I and 11 was given as 1946 through a typographical error but was twice correctly stated to be June, 1945, in the text referring to the Table. The small error in percentage reduction for seven-year-olds was also conceded. These points do not seriously underline the usefulness of the work(29).

Item 3: Re late commencement of National Health and Welfare study and detection of caries protection for young individuals born prior to commencement of fluoridation. Despite the fact that the Department of National Health and Welfare began its control study nearly three years after fluoridation began, much worthwhile information was obtained and the effect of late commencement, if any, was to result in underestimation of the fluoride protection(30).

Item 4: Reason for selection of control cities. It seems clear that Brown (1951) gave adequate reasons for selecting Sarnia and Brantford(31).

Item 5: Re superior dental care in Brantford. The difference in level of dental care between the cities is factual as recorded by Brown (1952). This variation of numbers of teeth classified as F. rather than D. or M. does not fundamentally influence the DMF rate(32).

Item 6: Comparability of rates. As stated under item 5, the dental condition of the children in Sarnia and Brantford differed in 1948 because a lower level of dental treatment in Sarnia resulted in higher tooth mortality. The tooth mortality rates thus differed but it does not follow that the DMF rates differed(33). Brown's statement (1951) "by 1948 the Brantford data were not greatly different from those in Sarnia" is obviously referring to DMF rates and hence quite valid(34). The differences in oral hygiene are also only remotely related to the DMF rates under discussion(35).

Item 7: Concentration of fluorides. The fluoride content of the Brantford water supply was raised to approximately 1 ppm in June, 1945, and raised to 1.2 in February, 1949(36) The Stratford water fluoride content is believed to have been in the order of 1.3 to 1.6 ppm since 1917 when the wells were drilled. Naturally no analysis for fluoride was available prior to the beginning of the interest in fluoridation and early techniques for analysis were not as reliable as present methods(37). These facts have been recorded in the writings of the primary workers (Hutton et al., 1951; and Brown et al., 1951, 1952, 1953, 1954, 1956) and the differences in amounts from other writers night seem less "strange" if they were merely acknowledged to be minor misquotations(38).

Item 8: Re statement by Brown et al. (1956). The statement is substantially correct with the exception that Brown's observational period did not begin until 1948 hence is less than 10 years(39). The decrease in mean df rates for the 9-11 years group in Sarnia between years 1948 and 1954 (Brown, 1956), did not continue into 1955(40). There was a highly significant decrease over the period 1948 to 1955 (2.37 to 1.93) in Brantford and no significant decrease in Sarnia (2.50 to 2.31)(41). In the same periods the mean df rates for this age [in] Stratford remained nearly equal (1.66 and 1.65) and increased for other ages (42).

Item 9: Re Table II: Ontario Department of Health Report. The printing of dashes rather than percentages for the control cities was to avoid confusing the table With "negative reductions" and in the case of the 9 to 11 df figure to avoid emphasising what was considered to be a spurious decrease(43). This judgment was borne out by the 1955 figures(44).

Item 10: Differences in reported rates between examiners. Different examiners give characteristically higher or lower rates upon examining the same individuals due to differences in skill, training the physical condition. Thus the differences quoted are no reflection on the design of the experiment or the care taken in the work. The strength of the double examinations comes through corroboration of caries trends in Brantford over the years and not through interchangeability of data(45).

Item 11: Significant fluctuations in controls. The important point is that for the controls the inter-year changes were upward trends or mere fluctuations (even though in some cases calculated to be beyond change), whereas in Brantford the change took the form of a highly significant continual downward trend(46).

Item 12: Larger percentage changes in control. There is no definite explanation as to why rates increased in Stratford and also in Sarnia over the ten years, but this may be a reflection of a general post-war increase in dental caries which has been seen in other areas. However, it is significant that in the various fluoridation experiments, e.g. in Brantford, Newburgh, Grand Rapids, etc., the shift has always been significantly downward in the fluoridated cities whereas the control city rates have remained about the same or in the case of Stratford, increased(47).

Item 13: Smaller percentage decrease after longer fluoridation. As pointed out by Sutton himself on page 168 (middle paragraph) the fluoride protection for permanent teeth of the children aged six to seven seemed to occur within two or three years after fluoridation began. Thereafter the yearly DMF rates were subject to random fluctuation and the differences in percentage decrease of 69 per cent and 51 per cent are most likely a reflection of this inter-year variation(48).

Item 14: The quotation from the Ontario Government Report is taken out of context from a series of summary statements. The previous statement was to the effect that in Brantford there had been a significant decrease of about 60 per cent in DMF rates. In the statement following, as picked out by Sutton, it was stated that "no change" occurred in Stratford and Sarnia(49). It should be clear enough from the context that the words "no similar downward change" were inferred(50).

Item 15: Possible weighting effect. The critic is referring to a possible shift in age distribution within the group, e.g. a possible sampling shift within the six to eight-year age group so that certain years had disproportionately higher or lower numbers of eight-year-olds and hence higher or lower average caries scores. This is rather remote in that selection methods used by Dr Brown were the same each year, moreover very large shifts in age distribution would be needed to produce the significant differences to which P N. R. Sutton refers(51).


Commentary on the Review by Dr R. M. Grainger

(26) Dr R. M. Grainger raises the question as to whether "the unimpeachable study can be done". This is, of course, unlikely. It is precisely for this reason that all papers (and these include my own) which set out to present new knowledge should be examined, in order to reduce the chance that findings which are not soundly based will be accepted at their face value. This is particularly necessary in those studies which may involve the health of the public.

(27) The result of Dr Grainger's attempt "to help set the record as straight as possible" will be judged after considering his other remarks.

(28) Item 1, Reference to Hutton et al. (1951); The numbers of children of the same age examined in the years 1944 and 1945 were very similar with the exception of the nine-year age group. From the unpublished data released at annual meetings in Brantford the number of children examined in 1944 was 239, and in 1945, 319; making a total of 558 (not 608). The data in Table I (Hutton et al.) were apparently combined by pooling the two years' results not by averaging the averages. However, the point is rather academic.

Comment. The phrase "making total of 558 (not 608)" suggests that the figure 608 was an error in this monograph. This is not the case, in fact this figure was not mentioned. It was published by the authors of this study, Hutton et al., in 1951 (Table 1, column 2). Dr Grainger, therefore, is suggesting that the total 558 children (derived from the unpublished figures of 239 and 319) is correct, and that the figure of 608 children examined, published by the authors of the study, is incorrect. It should be noted that, five years after this figure of 608 was first published, in Table II, column 2, of their final report Hutton et al. (1956) again published their figure of 608. In both the tables in which it appears it has been used in computing the def and the DMF rates. Also, if one accepted Dr Grainger's figure of 558 as the correct number of nine-year-old children examined in these two years, the impossible situation would also have to be accepted in which the number of these children with decayed, missing or filled teeth, which Hutton et al. (1951) gave as 595, would exceed the number of children examined.

(29) Item 2: Reference to Ontario Health Department report. The date of water-fluoridation in Tables I and II was given as 1946 through a typographical error but was twice correctly stated to be June, 1945, in the text referring to the Table. The small error in percentage reduction for seven-year-olds was also conceded. These points do not seriously undermine the usefulness of the work.

Comment. The "small" error in percentage reduction, which, Dr Grainger said "was also conceded", was the showing of 51 per cent instead of 66 per cent (p. 167). Dr Grainger does not mention here the substitution of dashes for figures in the two cases of reduction in the caries rate in the control cities (pp. 4, 37, 44). Several types of errors are present in Tables I and 11: (a) two omissions, which Dr Grainger implied-Item 9 of this review(43)-were made deliberately; (b) two typographical errors; (c) two arithmetical errors (Table I, age 7, "% Reduction Since 1944-45" in the caries attack rates should be 66, not 51, and in Table II, age 10, the "% Reduction Since 1944" in the caries attack rates should be 18, not 61); and if, as appears likely, the figures given by Dr Grainger in Item 1, of this review(28), are incorrect and were used, (d) four incorrect mean figures.

Dr Grainger contends that the points which he mentioned "do not seriously undermine the usefulness of the work"; but the occurrence, on one page alone, of all the errors and omissions which have just been mentioned certainly undermines confidence in the care taken in the preparation of this official report by the anonymous "statisticians" of the Division of Medical Statistics, Ontario Department of Health.

(30) Item 3: Re late commencement of National Health and Welfare Study and detection of caries protection for young individuals born prior to commencement of fluoridation. Despite the fact that the Department of National Health and Welfare began its control study nearly three years after fluoridation began, much worthwhile information was obtained and the effect of late commencement, if any, was to result in underestimation of the fluoride protection.

Comment. Dr Grainger does not state the nature of this "worthwhile information" but, whatever it was, it could not compensate for the lack of a pre-fluoridation caries assessment in this study. Its late commencement could be justified only if it was known that the caries rates in Brantford had not been affected by the ingestion of fluorides prior to the baseline examination (p. 168). However, the results from the City Health Department study, if taken at their face value, indicated that there had been marked and erratic changes: at first a considerable rise in the DMF rates after about one year of fluoridation, followed by a marked fall during the second year. It is surprising, therefore, that, out of all the cities in Canada, Brantford was chosen as the location of two long-term studies, for it should have been obvious that the value of the second study would be severely limited by the fact that the very important data showing the pre-fluoridation caries rates could never be obtained.

(31) Item 4: Reason for selection of control cities. It seems clear that Brown (1951) gave adequate reasons for selecting Sarnia and Brantford.

Comment. As Dr Grainger notes, this paragraph refers to the selection of the control cities, which were Sarnia and Stratford-not "Sarnia and Brantford". The sole reference to the selection of control cities which Brown (1951) gave is as follows: "The Ontario Dental Division, under Dr Frank Kohli, volunteered assistance, as did Dr G. L. Anderson, Medical Officer of Health for Sarnia, and Dr H. B. Kenner, Medical Officer of Health for Stratford, and both these cities entered the study as controls. (The water of Sarnia is fluorine-free, and that of Stratford contains 1.3 ppm. of fluorine from a natural source.)" Dr Grainger considers that "Brown (1951) gave adequate reasons" for the selection of the control cities-but few would agree with him.

(32) Item 5: Re superior dental care in Brantford. The difference in level of dental care between the cities is factual as recorded by Brown (1952). This variation of numbers of teeth classified as F. rather than D. or M. does not fundamentally influence the DMF rate.

Comment. Increased dental care usually includes some prophylactic treatments and, as noted by Doctors Blayney and Hill (18). even regular examinations may be accompanied by "more emphasis on the teaching of oral health." This statement by Dr Grainger implies that he considers that such increased dental care has no influence on the total DMF rate.

(33) Item 6: Comparability of rates. As stated under Item 5, the dental condition of the children in Sarnia and Brantford differed in 1948 because a lower level of dental treatment in Sarnia resulted in higher tooth mortality. The tooth mortality rates thus differed but it does not follow that the DMF rates differed.

Comment. It does not state "that the DMF rates differed; it points out, as its title states, the "Doubtful comparability of rates" owing to the delay in setting up this study. Dr Grainger's comments suggest either that he has not understood the meaning of the first sentence of the paragraph, or that he is seeking to distract attention from the presence of this important deficiency in the study-its late commencement.

(34) Brown's statement (1951) "by 1948 the Brantford data were not greatly different from those in Sarnia" is obviously referring to DMF rates and hence quite valid.

Comment. This quotation does not appear in Brown (1951) but a similar statement was made by Brown et al. in 1953 and 1954 (b) and is given on page 169. The fact that it was "obviously referring to DMF rates" was not questioned. The implications of this remark were discussed.

(35) The differences in oral hygiene are only remotely related to the DMF rates under discussion.

Comment. Brown et al. (1954b) said that "marked differences in oral hygiene as between the test and control groups might conceivably affect the findings". Such "marked differences" were reported - but were disregarded.

(36) Item 7: Concentration of fluorides. The fluoride content of the Brantford water supply was raised to approximately 1 ppm in June, 1945, and raised to 1.2 in February, 1949

Comment. This statement of Dr Grainger is welcome because it provides the answer to the question: Which of the statements regarding the concentrations of fluorides in the Brantford water, which were reported on page forty-two, are accurate and which ones are not?

(37) The Stratford water fluoride content is believed to have been in the order of 1.3 to 1.6 ppm since 1917 when the wells were drilled. Naturally no analysis for fluoride was available prior to the beginning of the interest in fluoridation and early techniques for analysis were not as reliable as present methods.<.p>

Comment. This statement is most revealing for it indicates that the wells at Stratford have been analyzed to determine their fluoride content only since "the beginning of the interest in fluoridation". If this is the case, the statements of Brown et al, (1953, 1956), concerning the "continuous" use of water containing fluorides in concentrations of 1.3 ppm or 1.6 ppm since 1917 are not founded on data and are, therefore, merely different guesses.

(38) These facts have been recorded in the writings of the primary workers (Hutton et al., 1951; and Brown et al., 1951, 1952, 1953, 1954, 1956) and the differences in amounts from other writers might seem less "strange" if they were merely acknowledged to be minor misquotations.

Comment. It was pointed out that the "facts" regarding fluoride concentrations were stated differently in these papers. In regard to the concentration in the Stratford supply, a comparison of the statements made by Brown et al., in 1953 and 1956 suggests that the concentration of fluorides in this supply may have increased from 1.3 to 1.6 in this three year period. The important admission that the fluoride concentration in Stratford was obtained only relatively recently, is not contained in any of the six "writings of the primary workers" mentioned by Dr Grainger. Therefore his statement is not correct.

As Dr Grainger suggests, it is not unlikely that the statements regarding fluoride concentration of the "other writers", the New Zealand Commission of Inquiry (1957) and the Ontario Department of Health (1956), were "minor misquotations".

(39) Item 8 Re statement by Brown et al (1956). The statement is substantially correct with the exception that Brown's observational period did not begin until 1948, hence is less than 10 years.

Comment. Dr Grainger suggests that the phrase "more than ten years" is incorrect. It was inserted into the quotation of a statement by Brown et al. (1956), but enclosed in square brackets to indicate that it was not a part of the quotation. However, in the sentence which immediately precedes that quotation Brown et al. (1956) said: "Brantford has had more than 10 years of experience with 1 part per million of fluoride in its water supply.During that time... "

It is clear that they were not referring to "Brown's observational period" of about seven years, but to the period of fluoridation in Brantford which commenced in June 1945 (Hutton et al., 1951; p. 173) and was, therefore, "more than 10 years".

(40) The decrease in mean df rates for the 9-11 years group in Sarnia between the years 1948 and 1954 (Brown, 1954), did not continue into 1955.

Comment. The 1955 rate of 2.31 df was still below the 1948 and the 1951 figures of 2.50 and 2.41 respectively.

(41) There was a highly significant decrease over the period 1948 to 1955 (2.37 to 1.93) in Brantford and no significant decrease in Sarnia (2.50 to 2.31).

Comment. The decrease mentioned by Dr Grainger (2.37 to 1.93) was reported in Brantford between 1948 and 1954 (Brown et al., 1954b) not "over the period 1948 to 1955". In 1955 this rate rose to 1.99 (Brown et al., 1956), and the difference between 1948 and 1955 was no longer said to be "highly significant" (Brown, 1955)

The rates quoted by Dr Grainger for Brantford are for the years 1948 and 1954 (see 63). It should be noted that it was between these two years that the maximum "decrease" was reported in the rates in that test city (2.37 to 1.93). Furthermore, in mentioning Sarnia, instead of giving the figures for the same period (1948-54), 2.50 to 2.11, he cited the figures 2.50 to 2.31, which cover a different period (1948-55) and do not reveal (Brown, 1955) the significant "decrease", in the rate in this control city, which was shown in the previous report (Brown et al., 1954b). By the use of these figures, the reviewer exaggerates the contrast between the test city and this control. Thus, this statement by Dr Grainger is both inaccurate and misleading.

(42) In the same periods the mean df rates for this age [in] Stratford remained nearly equal (1.66 and 1.65) and increased for other ages.

Comment. The rates for the four examinations were: 1.66, 1.76, 1.58, 1.65 (Brown, 1955). (Throughout this monograph caries rates have been given in the form in which they appear in the original papers although it is recognized that, in cases such as these, the practice of showing caries rates with two places of decimals is, probably, not warranted.) Dr Grainger mentions the least variable of the ten caries rates in the control cities-that for the deciduous teeth of children aged nine to eleven years in Stratford. He omits to mention the DMF rates which show the remarkable situation, in this control city, in which each of the inter-year changes occurring in this age group, and in five out of the six inter-year changes in the rates of the "other ages", were said by Brown (1955) to be statistically significant.

(43) Item 9: Re Table 11, Ontario Department of Health Report. The printing of dashes rather than percentages for the control cities was to avoid confusing the table with "negative reductions" and in the case of the 9 to 11 df figure to avoid emphasizing what was considered to be a spurious decrease.

Comment. This astonishing explanation, for the printing of dashes in this table, implies that these omissions were made deliberately because the results did not conform to those expected. Why should a decrease of 0.44 df (18 per cent) in the test city be accepted and published, but a very similar one of 0.39 df (16 per cent) in a caries rate in the control city of Sarnia be considered "spurious" and not published - a dash being shown in the appropriate position in the table? By printing these dashes, the "statisticians" of the Ontario Department of Health could have misled their Minister into thinking that there were no changes in these caries rates in Sarnia and Stratford (particularly as the Summary of the report said so) but that there had been a decrease of eighteen per cent in the corresponding rate in Brantford due to fluoridation.

Talk of "negative reductions" cannot disguise the fact that nothing is more calculated to confuse a table than (as Dr Grainger implies) the deliberate omission by "statisticians" of figures giving the percentage changes in rates (one of which was said to be significant).

(44) This judgement was borne out by the 1955 figures.

Comment. Dr Grainger tries to justify this "judgment" by implying that these so-called "spurious" decreases were not seen in the 1955 figures. However, small "decreases" were still shown in that year, the "reduction" in Sarnia being 7.6 per cent.

In any case, this so-called "judgment", regarding the omission of data, has no place in the preparation of an unbiased report.

(45) Item 10: Differences in reported rates between examiners. Different examiners give characteristically higher or lower rates upon examining the same individuals due to differences in skill, training the physical condition [sic]. Thus the differences quoted are no reflection on the design of the experiment or the care taken in the work. The strength of the double examinations comes through corroboration of caries trends in Brantford over the years and not through interchangeability of data.

Comment. Dr Grainger refers to the differences between examiners in the assessment of caries rates. This important matter has already been considered. The aim of the paragraph mentioned was to show that, as the rates obtained by the examiners in the two Brantford studies were different, data from the City Health Department study could not be used to decrease "the deficiency in the data of the National Health and Welfare study, owing to its late commencement"

The admission, which is implicit in Dr Grainger's remark, that "interchangeability of data" was not permissible between the two studies in Brantford confirms the point made. The degree of reliance which can be placed on the "corroboration of caries trends in Brantford over the years" must be considered in the light of the widely divergent results obtained in these studies, which were discussed in the second paragraph of page three.

(46) Item 11: Significant fluctuations in controls. The important point is that for the controls the inter-year changes were upward trends or mere fluctuations (even though in some cases calculated to be beyond change) [sic], whereas in Brantford the change took the form of a highly significant continual downward trend.

Comment. It was pointed out that in the control city of Stratford five out of the six comparisons made between the permanent teeth rates of successive years were said by Brown et al. (1954b) to be significant changes (four of them being at the three standard error level). In the permanent teeth rates in the other control city, Sarnia, there were four highly significant and one significant change in the nine comparisons made. Brown et al. (1953, 1954b) and Brown (1955) said that the odds relating to the occurrence by chance or sampling variation of a difference of the magnitude of three standard errors (such as were reported in eight of these changes) "are 369 to 1 against". Therefore, when Dr Grainger terms these unexplained changes "mere fluctuations" he is rejecting that remark of Brown et al. and denying the meaning of statistical significance.

Dr Grainger neglected to mention that the "highly significant continual downward trend" in the caries rates in Brantford occurred only in children who were aged twelve to fourteen years. In the two other age groups, in both the deciduous and the permanent dentitions, there was an upward trend in the caries rates in the fluoridated city during the last year of the study, the rise from 0.44 DMF to 0.69 DMF, in the youngest age group, being said to be a highly significant rise (Brown, 1955). Therefore this statement by Dr Grainger, that there was a "continual downward trend" in Brantford, is incorrect and is misleading.

(47) Item 12. Larger percentage changes in control. There is no definite explanation as to why rates increased in Stratford and also in Sarnia over the ten years but this may be a reflection of a general post-war increase in dental caries which has been seen in other areas. However, it is significant that in the various fluoridation experiments e.g. in Brantford, Newburgh, Grand Rapids, etc., the shift has always been significantly downward in the fluoridated cities whereas the control city rates have remained about the same or in the case of Stratford, increased.

Comment. Dr Grainger's statement, that the "rates increased in Stratford and also in Sarnia over the ten years", is inaccurate for, as he pointed out in his Item eight (39), "Brown's observational period did not begin until 1948, hence is less than 10 years." Sarnia was first examined in March 1948 and Stratford in October of that year (Brown, 1952). Therefore the caries rates of the children in both those towns were known for a period of about seven years, not one of ten years. Furthermore, in the deciduous teeth in Sarnia, the younger age group showed a higher rate in 1955 than in 1948, but in the older children the final rate was lower than the initial one. In this city the DMF rate rose between 1948 and 1953 but between that year and 1955 there was a decrease in this rate in each of the three age groups.

The suggestion that there has been "a general post-war increase in dental caries" is not supported by these studies, for such a rise it was not seen in any of the unfluoridated control cities considered. In Muskegon and Oak Park there was no definite trend. At the time when (as a result of their being fluoridated) these cities ceased to serve as controls, the rates for the children of some ages were higher, and for other ages they were lower, than during the initial examination. The trend in Kingston cannot be investigated owing to the method of presenting the data in the Newburgh study. The contention that "the shift has always been significantly downward in the fluoridated cities" can be accepted only if the many deficiencies pointed out in this monograph are ignored and the figures from these trials accepted at their face value.

(48) Item 13: Smaller percentage decrease after longer fluoridation. As pointed out by Sutton himself on page 168 (middle paragraph) the fluoride protection for permanent teeth of the children aged six to seven seemed to occur within two or three years after fluoridation began. Thereafter the yearly DMF rates were subject to random fluctuation and the differences in percentage decrease of 69 per cent and 51 per cent are most likely a reflection of this inter-year variation.

Comment.No specific mention was made of "the children aged six to seven" when pointing out the reductions in the DMF rates which were reported to have occurred in the early years of the City Health Department study (Hutton et al., 1951). Some implications of this reported early decrease in caries rates were discussed on pages two and thirty-eight.

When he makes the remark that "the differences in percentage decrease of 69 per cent and 51 per cent are most likely a reflection of this inter-year variation", Dr Grainger shows that he could not have noted that the increase in the DMF rate in these children, in the fluoridated city, from 0.44 in 1954 to 0.69 in 1955 (so that the "percentage decrease" dropped from 69 per cent to 51 per cent), was shown by Brown (1955) to be, statistically speaking, a highly significant (three standard error level) rise in the rate in the test city during the final year of the study. Therefore, when he makes this suggestion, he is expressing an opinion which contradicts the notation given by Brown (1955), in his Table IV, which indicates that the rise in rates which produced this percentage "decrease" is statistically significant at the three standard error level.

Dr Grainger may be right-but if he is, Brown's (1955) indication of statistical significance in this case is incorrect, and the methods used in the National Health and Welfare study for calculating statistical significance must be questioned. In consequence, all statements made in the study regarding significant changes in the caries rates, both in the test city and its controls, become doubtful.

It is of interest to note that the "1955 Report" from this study was released in two different publications. The first, a booklet, was dated November 1955, and was "prepared by H. K. Brown ... with the assistance of H. R. McLaren... G. H. Josie... and Barbara J. Stewart". The second publication is a paper by Brown, McLaren, Josie and Stewart published in 1956 in the Canadian Journal of Public Health, no reference being made to the previous publication. The ten tables and the two figures in the body of these reports are the same and the text of both is practically identical. However, there is one important difference: that part of the discussion dealing with the unexplained rise (shown as significant) in the DMF rate of children aged six to eight years in Brantford (and also in the control city with the "optimum" concentration of fluorides in its water), was omitted from the later report (Brown et al., 1956).

The questions should be asked: Why was this very important small section of the original report omitted when it was published in the Journal? Why, in both these 1955 reports, was the smaller percentage "decrease" between the initial and the final caries rates of the youngest age group in Brantford not published?

(49-50) Item 14 The quotation from the Ontario Government Report is taken out of context from a series of summary statements. The previous statement was to the effect that in Brantford there had been a significant decrease of about 60 per cent in DMF rates. In the statement following, as picked out by Sutton, it was stated that "no change" occurred in Stratford and Sarnia(49). It should be clear enough from the context at the words "no similar downward change" were inferred(50).

Comment. The charge that the quotation mentioned was "taken out of context" is meaningless unless it implies that the sense of the original statement has been altered. So that the reader can judge this matter, the whole of paragraph three (the "previous statement" referred to by Dr Grainger) and paragraph four are reproduced. The quotation given on page 176, which was the one criticized, is shown here in italic type to distinguish it from its context.

The evidence produced by the investigators of the Brantford City Health Department and of the Department of National Health and Welfare, independently show that since the introduction of the fluorine in the water there has been a significant decrease, amounting to approximately 60 per cent in the number of decayed, missing and filled teeth suffered by Brantford school children.

At the same time, "it has been established that there has been no change in the already low dental caries attack rates in Stratford which has 1.2 ppm of natural fluoride in its domestic water, or in the relatively high rates for Sarnia which has had virtually no fluoride in its water."

Dr Grainger suggests that the writers of this report, when they used the expression "no change", really meant "no similar downward change". However, as they were members of the Division of Medical Statistics and, presumably, were trained in the very precise science, of statistics, it is unlikely that they would use such an inexact expression. Also, the term "downward change" is a rather clumsy substitute for the word "decrease" which was used in the previous paragraph (para. 3 above). Both these points suggest that Dr Grainger's interpretation is incorrect.

(51) Item 15 Possible weighting effect. The critic is referring to a possible shift in age distribution within the group, e.g. a possible sampling shift within the six to eight-year age group so that certain years had disproportionately higher or lower numbers of eight-year-olds and hence higher or lower average caries scores. This is rather remote in that selection methods used by Dr Brown were the same each year; moreover very large shifts in age distribution would be needed to produce the significant differences to which P N. R. Sutton refers.

Comment.After reading Dr Grainger's remarks it may be supposed that it was said that the inter-year significant changes in caries rates, reported from the control cities, were due to a "weighting" effect. However, if the original paragraph is consulted, it will be found that it is headed "Unexplained Significant changes in controls." A "weighting" effect was mentioned as a possible explanation for these unexplained changes. This suggestion was made following the failure of the authors (Brown, 1951, 1952; Brown et al., 1953, 1954b, 1956) to advance even a suggestion why these changes occurred. Dr Grainger's comment leaves these significant changes in the caries rates of the control cities as the authors of this study left them - unexplained.

This reviewer has made it clear that the statements regarding the "continuous" use of water containing fluorides in concentrations of 1.3 or 1.6 ppm since 1917 in Stratford are not based on data (comment 37); and that the misleading omission of figures from the Ontario Department of Health Report (1956) was made deliberately (comment 43). However it has been seen that, although Dr Grainger said (27) that his aim was "to help set the record as straight as possible", most of his comments, if they had been accepted at their face value, would have had the reverse effect.


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