Reviewer's report
Title:A Prospective study of the association between weight changes and
self-rated health
Version: 1Date:20 November 2007
Reviewer: C Schooling
Reviewer's report:
General
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Major Compulsory Revisions (that the author must respond to before a decision
on publication can be reached)
1. It would be very helpful if the analysis could be clarified.
a) It is not clear how the change in BMI exposure is defined. Change of two BMI
units is used in the abstract results and mentioned in the statistical analysis (1st
line on page 7), but Table 2 presents BMI change as change in BMI category
(<18.5, 18.5-<25 and 25 plus).
b) Table 2 presents the association of change in BMI category with SRH stratified
by baseline BMI category. The rationale for this stratification should be explained
in the methods. Given the very large number of women in the normal weight
category, it might be more helpful to categorize weight change in terms of lost
2.25kg or more, lost <2.25kg, no change or gained <2.25 kg, gained #2.25kg &
<4.5kg, gained >4.5kg, as in a previous similar study. (Williams LT, Young AF,
Brown WJ. Weight gained in two years by a population of mid-aged women: how
much is too much? Int J Obes (Lond). 2006 Aug;30(8):1229-33.) With this
approach the authors could also formally test whether the effect of weight loss
varies with baseline weight status.
c) Table 3 presents the association of SRH health in 1993 with BMI change for
women with normal weight in 1993. However, the “variables included in the
analysis section” says that in this situation the exposure variable was “change in
SRH”.
2. Some information about the women lost to follow-up would be useful. For
example, are they similar to the women included in the study?
3. It would be helpful if the background to the study could be clarified and a more
thorough comparison made with the existing literature. For example, there
appears to be some literature suggesting that weight loss has more benefits for
physical than mental health.
4. Given both change in BMI and change in SRH are described as exposures,
Table 1 should show the baseline characteristics by change in BMI (as it does)
and by change in SRH.
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Minor Essential Revisions (such as missing labels on figures, or the wrong use of
a term, which the author can be trusted to correct)
1. p3 The first two odds ratios in the abstract results do not match any of the
results presented, is this correct? In addition it would be helpful to know whether
these are raw or adjusted odds ratios.
2. p6 Potential confounders section, it says “Age was stratified in <49 years..”,
however it looks as if age was categorized no stratified.
3. p6 Statistical analysis “and potential mediating factors were analyzed.
Potential mediating factors such as changes in..” however, I can’t see any further
use made of information about changes in physical activity and or any other
factors, although it looks as if Tables 2 and 3 were adjusted for baseline values
of these factors. It might be best to remove this section about mediating factors.
4. p7, lines 4-5 is this statement correct “Therefore, we analyzed the association
between changes in SRH and changes in BMI-categories”
5. p15 please clarify the heading of Table 2 does ‘poor health’ mean ‘poorer
self-rated health in 1993 than 1999’?
6. p8 is Table 3 adjusted for covariates? The footnote implies that it is, but the
sentence in the middle of page 8 ‘When we controlled for covariates such as
smoking, diet…, the general pattern of association did not change’ suggests that
it is not.
7. p9 “Health related quality of life and SRH may be two different measures and
therefore not comparable”, could the authors explain how differences in these
measures could have resulted in different findings.
8. p9 ‘[we] controlled for mediating factors..’ Is this correct?
9. p9-10 “mediating factors, such as changes in the use of general practioner,
changes in physical activity, changes in fruit and vegetable consumption and
changes in smoking status did not have an effect on the association between
exposure and outcome” Is this sentence referring to analysis given in the results
section or to an additional analysis?
10. p11 Discussion of their findings about baseline SRH and weight gain should
be in the main discussion section (before Strengths and Weakness) not in the
Conclusion section.
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Discretionary Revisions (which the author can choose to ignore)
What next?: Unable to decide on acceptance or rejection until the authors have
responded to the major compulsory revisions
Level of interest: An article whose findings are important to those with closely
related research interests
Quality of written English: Needs some language corrections before being
published
Statistical review: No, the manuscript does not need to be seen by a
statistician.
Declaration of competing interests:
I declare that I have no competing interests