Reviewer's report
Title:Risk of menstrual disorders among female registered nurse: a nationwide
retrospective cohort study in Taiwan
Version:2Date:31 March 2015
Reviewer: Elizabeth Bertone-Johnson
Reviewer's report:
Comment on Risk of menstrual disorders among female registered nurses: a
nationwide retrospective cohort study in Taiwan.
This article presents data comparing the incidence of clinical diagnosis of several
menstrual disorders among registered nurses with incidence among general
population controls. The authors propose that risk of many menstrual disorders
should be higher in nurses than other women due to job strain, rotating night
shifts and other occupational factors.
Major compulsory revisions:
1) Additional clarifications on the selection of cases from the Taiwan NHIRD
would be helpful to the reader.
2) How frequently would women experiencing menstrual disorders seek
treatment and thus receive a ICD diagnosis in their medical file? In many
populations, only women who experienced very severe symptoms, long-duration
symptoms or consequences/correlates of symptom experience such as infertility,
anemia, fibroids, etc would seek treatment and have menstrual disorders
recorded in their files. It is also likely that women would seek treatment for some
disorders more often than others, and that nurses would be more likely to seek
treatment than women not in health care professions. Please comment on the
overall likelihood that clinical diagnosis and the presence of an ICD code in
medical records is a valid way to identify cases, and that absence of ICD code is
a valid indicator that a woman is not experiencing these menstrual disorders.
Otherwise, this means of determining outcomes will result in substantial
misclassification. The authors allude to this in their discussion, but a more
detailed assessment of the likelihood of misclassification is needed.
3) The authors state that “at least two diagnoses of the same menstrual disorder
that occurred within 30 days were considered a definitive diagnosis.” While I
appreciate that this will result in a considerably more rigorous case definition, it
seems unlikely that many women would be seen in a clinic twice within a single
30 day period and have the same diagnosis reported. Thus, the 30 day
requirement seems overly restrictive. It seems more reasonable to assume that
women might receive the same diagnosis multiple times within a year or two- the
authors might consider relaxing their definition to include a longer period for case
confirmation.
4) Also, for women receiving only one diagnosis but not meeting case definitions,
did these women remain in the analysis as non-cases or were they censored at
the time of their first diagnosis?
5) Were controls matched to cases on follow-up duration as well as index date of
entry into the cohort?
6) Additional information should be provided on the statistical modeling
approach, and the interpretation of results from the Cox model. Why did the
authors choose to model the log of time vs. only time? Why did they choose to
model main effect + time + interaction term, as opposed to stratifying by time and
evaluating the main effect across strata? The latter approach would likely lead to
more interpretable estimates of the HR. With the current modeling approach, it is
unclear how to interpret the interaction effect of time x group and the main effect
for group in the context of the interaction term. Please consider stratifying by time
and reporting HR across time strata.
7) In the Discussion, the authors conclude that “the hazards of a number of
menstrual disorders were significantly higher in nurses compared with the
general population” and then list 6 menstrual disorders. However, wasn’t risk
significantly lower for many of these conditions, at least during much of the
follow-up period? Please revise the Discussion to clarify the effects of group and
time.
8) Please comment on how the incidence rates of the menstrual disorders
evaluated here compared with prior studies and population-level data. This
information could be used to reassure readers that the use of ICD codes to
identify cases leads to comparable information as longitudinal studies repeatedly
assessing the presence or absence of menstrual disorders.
Level of interest: An article of limited interest
Quality of written English: Acceptable
Statistical review: Yes, and I have assessed the statistics in my report.
Declaration of competing interests:
None