PONE-D-19-17898

Gender differences influence over insomnia in Korean population: A cross-sectional study

PLOS ONE

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"Yun Kyung La has no conflicts of interest to declare.

Choi Yun Ho has no conflicts of interest to declare.

Min Kyung Chu was involved as a site investigator for a multicenter trial sponsored by Otsuka Korea, Novartis International AG and Eli Lilly and company. Min Kyung Chu worked an advisory member for Teva and received lecture honoraria from Allergan Korea and Yuyu Pharmaceutical Company in the past 24 months.    

Jung Mo Nam has no conflicts of interest to declare.

Young-Chul Choi has no conflicts of interest to declare.

Won-Joo Kim has no conflicts of interest to declare."

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Reviewer #1: Yes

Reviewer #2: Yes

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2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: I Don't Know

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Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: Yes

Reviewer #2: Yes

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5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: This is a cross-sectional study aiming at the gender differences of insomnia symptoms. The findings and conclusions are not new while the methodology sounds satisfactory. The findings in the current study confirmed gender differences in insomnia and its subtype in Korean population. The strengths of the study include a reasonable measurement tool and good sampling framework, despite a lack of details. I have some suggestions for the authors.

1. What is the validity for each questionnaire in Korean version? Especially for ISI and PSQI.

2. The two-stage clustered random sampling method proportional to the population and socioeconomic distribution for all Korean territories should be presented in more details. Residents from which area were randomly selected?

3. When was the study conducted?

4. The response rate was poor, which should be considered a significant limitation.

5. Gender steroids should be rephrased as “sex steroids”. In general, gender is a more sociology concept while sex is a more biology concept.

6. Another explanation for the gender difference of insomnia is the gender difference in somatic perception.

Reviewer #2: Thank you for this chance to review this interesting manuscript, titled “Gender differences influence over insomnia in Korean population: A cross-sectional study”. This manuscript reported on the prevalence and associated factors of insomnia/symptoms in a sample of 2,695 Korean Adults. It was found that insomnia symptoms were present in 10.7% of survey respondents, and were positively associated with female gender, shorter total sleep duration, and psychiatric co-morbidities/symptoms. This is an interesting study which replicates data of previous studies in the general population of Korea. Its major strengths are the large sample size and reporting of results in the Korean population. My main concern is the limited amount of novel data/findings presented in this manuscript. As this is such a potentially rich dataset and study, I’ve tried to give some general comments/questions to investigate some more novel data.

Major:

·       Non-restorative sleep is no longer included among insomnia disorder criteria (or subtype). Consider removing and focusing only on DIS, DMS, and EMA subtypes/criteria for insomnia disorder.

·       What item of the ISI was used to determine NRS? Unless an additional item was included, I don’t think any of the items assess NRS (Dis/satisfaction, Noticeable to others, worry, and daytime functioning interference).

·       Abstract: Method section, page 6 description of the ISI, etc. The ISI should not be used in isolation to ‘diagnose’ insomnia. Consider re-wording to ‘classify’ insomnia rather than ‘diagnose insomnia’ in these sections.

·       Consider selection/response bias (of the 7,430 individuals approached, is it anticipated that more/less respondents with insomnia symptoms self-selected to complete the survey?

·       Table 3. Multivariate regression analysis, examining effect of gender, while controlling for gender as co-variate? The different models/co-variates may require review from a statistical reviewer. I may have mis-read something here.

·       The last 3 items of the ISI may be confounded with measures of depression/anxiety. I wonder whether the association between the ISI and psychiatric symptoms could be driven by the overlap in symptoms assessed by these items? It may be interesting to examine a ‘night time insomnia symptom’ group, using a composite score on the first 3 or 4 ISI items only, and re-examining relationships with anxiety/depression. This could be reported in a sensitivity analysis confined to the supplement.

·       Consider a sensitivity analysis removing the “difficulties falling asleep, staying asleep, etc” question from the PHQ-9 and investigating whether the relationship between the PHQ and ISI is reduced. Shared symptoms may increase relationship here without truly reflecting a positive association between insomnia and depression.

·       Same for the ‘sleep’ items of the Goldberg Anxiety Scale.

Minor:

·       Minor grammatical changes throughout (‘symptom’ vs ‘symptoms’, etc.).

·       Consider clearly differentiating “Insomnia disorder” (chronic and frequent night-time symptoms, plus daytime functional impairments), and “Insomnia symptoms” (night time complaints only) early in the manuscript.

·       Page 9, “Prevalence of insomnia and poor sleep quality’ section – There is a potential for some wording confusion in the second and third sentence. Please consider modifying the final sentence (“182 (6.8%) were accompanied by DIS…”) to specify that the denominator was the total 2,695 participants, not the 715 participants with PSQI of 5+.

·       Consider collapsing the multiple sub-headings in the Results section into a single sub-heading (e.g. several sections report gender differences for different outcomes/definitions).

·       Supplement Tables 1, 2, correct to ‘difficulty initiating/maintaining/etc sleep’

·       Other studies have reported a greater incidence of EMA, but lower incidence of DIS in older adults. It may be interesting to make comparisons in the discussion section.

·       What is the state of treatment services for insomnia in Korea? If 10% of the population suffer from insomnia symptoms, will more resources be required to treat them? May be worth commenting on these aspects in the discussion.

Additional Considerations and other Analyses

·       Separate cohort into different age brackets and examine prevalence of different insomnia complaints (e.g. <30, 31-40, 41-50, etc.).

·       It would be interesting to present a figure of changes in the three insomnia subtypes by age.

·       Did you collect any measure of employment (either job area, work hours/week, sick leave, etc.)? This may make an interesting comparison between insomnia/no-insomnia symptoms groups.

·       Any additional measure of other medical/psychiatric co-morbidities?

·       It may be interesting to also include a different ISI cut-off to define “Moderate” or “severe” insomnia (in addition to insomnia symptoms ISI >9.5). I wonder whether your gender and age effects will persist with different definitions of insomnia.

·       Consider examining TST between weekends and weekdays in both insomnia and no-insomnia participants. Is it possible that there is a greater discrepancy between weekends/weekdays for insomnia sufferers but not for those without insomnia symptoms. It would be interesting to examine the effect of age here too.

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Reviewer #1: No

Reviewer #2: No

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Gender differences influence over insomnia in Korean population: A cross-sectional study

PONE-D-19-17898R1

Dear Dr. Kim,

We are pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it complies with all outstanding technical requirements.

Within one week, you will receive an e-mail containing information on the amendments required prior to publication. When all required modifications have been addressed, you will receive a formal acceptance letter and your manuscript will proceed to our production department and be scheduled for publication.

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With kind regards,

Masaki Mogi

Academic Editor

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Additional Editor Comments (optional):

The authors well responded to the Reviewers' comments.

Reviewers' comments:

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Comments to the Author

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Reviewer #1: All comments have been addressed

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2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

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3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: (No Response)

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4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: (No Response)

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5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: (No Response)

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6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: (No Response)

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7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

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Reviewer #1: No