Reviewer's report
Title:A Prospective study of the association between weight changes and
self-rated health
Version: 2Date:12 March 2008
Reviewer: C Schooling
Reviewer's report:
General
This revised version is much clearer and easier to understand than the previous
version. There are still some parts of the manuscript which are hard to follow,
and I still have some outstanding queries about the methods and interpretation of
the data.
Minor Essential Revisions (such as missing labels on figures, or the wrong use of
a term, which the author can be trusted to correct)
Abstract
1. Aims, 1st sentence, is it correct that all the women were ‘healthy’ at baseline?
2. Aims, 2nd sentence, should read “We also examined if poor SRH at baseline
was associated with later weight gain”
Research methods
1. Statistical analysis. The first sentence says that they used stepwise
regression. The second sentence says that they included all variables with a
p-value<0.25 in univariate analysis. So, I assume that they first selected their
confounders then used stepwise regression, which might have dropped a few
more confounders. Is this correct? Tables 4 and 5 include the same confounders,
which would seem unlikely if they had used stepwise regression in several
different analyses. Anyway, given their very large sample size it would probably
be better just to include all the potential confounders.
2. The section “variables included in the analysis” is difficult to follow. Maybe
re-arrangement of the text with sub-sections headed ‘Exposures’ and ‘Outcomes’
would make it easier to follow.
Results
1. Please could the authors check why there are 1190 women missing from
Table 3. Table 1 shows SRH change for all 13684 women, Table 2 shows BMI
change for all 13684, so I would have thought there should be the same number
of women in Table 3, showing SRH change by BMI change. However, I am not
sure that Table 3 is really necessary.
2. Given that the authors have clarified that they using baseline SRH as one of
the exposures, they should provide a table similar to table 2 showing baseline
SRH as columns and other baseline characteristics as rows.
3. In tables 4 and 5 the authors show the adjusted risk of a reduction in self-rated
health by change in BMI. Table 5 shows that both weight gain and weight loss
are associated with a reduction in SRH. In contrast, Table 4 shows that weight
gain in the underweight is associated with an increase in SRH, but weight gain in
the normal weight is associated with a reduction in SRH. Similarly weight loss in
the normal weight is associated with a reduction in SRH, whilst weight loss in the
overweight is unrelated to SRH. I may have mis-understood both these tables,
however it would be helpful if the authors could clarify whether they think that
weight change always has the same effect on SRH, or whether they think that
the effect of weight change on SRH varies with initial weight status. I realize that
this later question is not part of their stated aims, however, they have presented
results concerning that question. Essentially, the authors should choose between
presenting Table 4 or Table 5, which would also help simplify the ‘variables
included in the analysis’ section. Depending on whether they chose to present
Table 4 or Table 5, the abstract, results and the discussion should be amended
accordingly.
Discussion
4. The authors have removed a section concerning regression to the mean. This
section should have been better explained rather than removed.
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Discretionary Revisions (which the author can choose to ignore)
Please can the manuscript be re-checked for spelling and grammar.
What next?: Accept after minor essential 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'