Review for 10.1186/s12876-015-0236-z (2015)

Reviewer's report
Title:Increased use of hypnotics in individuals with celiac disease: A nationwide
case-control study
Version:1Date:18 November 2014
Reviewer: Fredrik Norström
Reviewer's report:
General comment
The article is very well-written. The approach from the authors seems to well
describe the relationship between use of hypnotics and celiac disease. The
authors also well motivates their findings and the implications of their results from
their point of view. The article is unique and adds important and relevant
information to the field.
Still, I have some details I want the authors to improve.
Major compulsory revisions
Methods
1. It is not described how controls have been assigned to cases. It is almost but
not exactly 5 controls per case. If it is 5 controls per case, the reason for not
being exactly 5 controls per case is likely to be due to missing data. If so, this
needs to be mentioned as it is even more important to explain why the rate is not
exact in a matched case-control study and also what the implications might be.
2. The description of conditional logistic regression needs to be improved. It is
highly recommended to add a reference to the method. It is not a standard
statistical method that any reader can be supposed to know and understand how
it works.
Minor revisions
Abstract
1. The wording “unchanged risk estimates” at row 30 is unclear. Does it refer to
the odds ratio being similar as the unadjusted odds ratio or does it refer to the
odds ratio not being significant. In either of the cases, the expression should be
improved. My guess is that refers to 1.23 being unchanged in comparison to
1.33. It is “similar” but cannot be considered to be unchanged.
2. The presentation of first “unadjusted” estimate (row 27-28) of insomnia in
relation to celiac disease and thereafter “adjusted” estimates (row 30-33) is poor.
It might be motivated to formulate that neither psychiatric comorbidity nor restless
legs syndrome are contributing as confounding variables in the relationship
between insomnia and celiac disease and to include ratios in the presentation.
As it is now formulated it is only used to repeat main result with more or less
trustworthy estimates as they do not change things according to authors.
Methods
3. It has not been motivated why # 2 prescriptions of hypnotics is chosen as
cut-off.
Results
4. On row 181-182 it is written “with no change in risk estimates”. This is not
correct as the risk estimate differ from previous estimate. This needs to be
reformulated. Wordings like “similar” would probably work fine.
Tables
5. Missing end (Melatonin … for controls) and start parenthesis (ages 40-59 for
cases) in Table 2.
6. Should # 3 courses of hypnotics instead be # 3 prescriptions of hypnotics? If
so, correct it, else “courses” must be defined in the article. It is also unclear if # 3
prescriptions is compared with <3 or <2 prescriptions. As the authors mentions
dose-response it might be compared with <2 prescriptions.
Discretionary revisions
Background
1. The authors focus on insomnia in the background. The authors have not
access to good data about insomnia and instead use prescriptions of hypnotics
as a good indicator of insomnia. For such reason they also use hypnotics in the
title of the article. However, the background have not discussed hypnotics at all.
It would be valuable if the authors can include information about how well
prescriptions of hypnotics predict insomnia.
Methods
2. The phrasing at row 115-117 gives the impression that sleep apnea and
restless leg syndrome are very similar diseases, and that studies for restless leg
syndrome strongly indicate what results to be expected for sleep apnea. This
sentence would benefit from being rewritten. If they were that strongly correlated
the authors would not do independent analyses for the two conditions.
Figure
3. Figure 1 presents information about how many that were excluded due to a
biopsy performed between 1969 and 2004. The article focus on biopsies
between 2005 and 2008. I don’t think that it is relevant enough to highlight
individuals that does not fulfil inclusion criteria. It is relevant to explain the
selection in methods section though. It might have been nice to highlight the
numbers due to the sub-analysis but this neither includes all with a biopsy from
1969 to 2008. Additional file 1 better presents how analyses were performed. It
might be a good idea to replace Figure 1 with additional file 1 and perhaps also
add information from additional file 2 if it is considered important to highlight
which individuals that were selected for this analysis.
Level of interest: An article whose findings are important to those with closely
related research interests
Quality of written English: Acceptable
Statistical review: Yes, and I have assessed the statistics in my report.
Declaration of competing interests:
I declare that I have no competing interests