Reviewer's report
Title:A Prospective study of the association between weight changes and
self-rated health
Version: 1Date:4 November 2007
Reviewer: Yael Benyamini
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)
The study addresses important questions regarding the association between
weight and SRH and in particular between changes in these measures. The data
was derived from a large longitudinal study, which is appropriate for the test of
these questions. However, the data was handled in way that simplifies the
analyses and their presentation but undermines the validity of this study. This
could be corrected.
Main concerns: The method and results sections are difficult to follow; the
dichotomized measures do not provide only a very partial test of the hypotheses,
which does not allow one to reach sound conclusions.
Detailed comments:
Introduction
Needs to be re-organized. After the background on obesity, it would be helpful to
briefly present the main research question; then the rationale for the hypotheses;
and then the hypotheses.
The sentence that begins on line 11 (“Individuals who rate…”) needs a reference
or a statement that this is the current research question.
Next sentence – the hypotheses are presented before the rationale for them.
Next sentence, mention of 1993 and 1999 – this is part of the procedure of the
specific study, which the reader is not familiar with yet, and should not be
presented before the theoretical background is fully presented,
The next sentences provide a rationale for the hypotheses and should be
presented before them.
Methods/Results
The main problem is that most measures were dichotomized, thus losing a lot of
information. In the case of SRH this does not seem to be justified, even though it
simplifies the analyses and the presentation of the findings. The authors state
that SRH was dichotomized into optimal (good or very good) and suboptimal (fair
or below) and changes in SRH were dichotomized as better or worse. Was better
or worse defined as a move between all five original SRH responses or between
the two categories created later? It is impossible to understand this from the
method section, which needs to be written more clearly, but this is what I
understand from the first paragraph of the results section. If indeed so, this is too
rough a measure: Only moves that cross the fair to good line count as changes.
It would be best to repeat the analyses using the full BMI and the full SRH
scales. The results from such analyses should at least be reported in the text, if
they end up pointing to similar conclusions, and should be presented in full if they
reveal a more complex picture than the one currently presented.
In general, it is difficult to understand when the baseline measures were used
and when change measures were used.
Does Table 2 refer to poor SRH at baseline?
Discussion
The analyses need to provide a better test of the hypotheses (see comments
regarding dichotomization of variables), in order to reach some of the
conclusions listed here.
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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)
General: Many of the paragraphs are much too long and need to be broken down
in relevant places.
Method
Exclusion of women above 69 – describe why.
Only three chronic diseases were used as potential confounders – if the authors
have information about additional diseases, it would be good to add them (or add
a count of the number of chronic diagnoses).
More detail is needed on the measures (e.g., what is ‘influence’, in the
psychosocial work environment questions). What were the original questions?
(the wording of the questions and the response options).
Please explain how the interactions were tested.
Results
Provide standard deviations for age and height.
Table 1 is very difficult to follow.
First paragraph of the results section: “The table shows an effect…” – table 1 is
purely descriptive and therefore does not describe effects. It is possible and
recommended to add univariate tests to the manuscript.
Table 3 – were those who lost weight excluded from this analysis or included in
the reference category?
Discussion
Discussion of reference 9, which reported results contradictory with those of the
current study – the explanation provided (ref 13) may not be the only one; was
the study in ref 9 carried out with the same population and methods as the
current one?
Regression to the mean – the explanation is either inaccurate or should be better
explained to the reader.
Too many limitations are listed. The authors should list the main relevant ones
and explain how they are relevant to the current study (for example, the study
does not include very old or very young people; this does not mean that
dichotomization did not result in loss of information; another example, it is
enough to state that there may be other correlates of SRH that are also related to
weight and weight changes and were not measured in this study and give
examples of general categories (e.g., personality traits).
There are quite a few typing and language errors that should be corrected.
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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 of importance in its field
Quality of written English: Needs some language corrections before being
published
Statistical review: Yes, and I have assessed the statistics in my report.
Declaration of competing interests:
I declare that I have no competing interests.