Napping Behaviors and Extracurricular Club Activities in Japanese High School Students: Associations with Daytime Sleep Problems

Round 1

Reviewer 1 Report

Napping behaviors and extracurricular club activities in Japanese high school students: Associations with daytime sleep problems

Line 32 there is an additional, new study on a large sample of adolescents that should be considered: Sleep Medicine, 2019, May, Breakpoints of time in bed, midpoint of sleep, and social jetlag from infancy to early adulthood.

Line 45: yes, this seems true. Please see also Rahafar et al. 2019 Biol Rhythm Research. These people provide a new measurement like midpoint of napping, and they show that later napping results in later bedtimes. I am not sure which variable influences the other, but it might be also some kind of feedback process: by loosing sleep, adolescents nap, which in turn, delays their bed time, some kind of vicious circle.

Line 64: please specify the factors, not just write “some other”. Because every relevant factor in your study needs to be introduced in the introduction.

The variables assessed seem to be sufficient.

Also, the analyses seem to be correct, with the most interesting one being the logistic regression.

Probably, some or a few of the Tables could be moved to the supplementary information because there are too many tables. But I would leave this decision to the authors/editors, which tables.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

The authors provide a brief report of a study investigating the relationship between various daytime variables including napping behavior, the engagement in extracurricular activities, and other daily activities on sleep problems. The ideas behind the study are compelling – that those involved in extracurricular activities are more tired, which results in more late evening napping behavior which then interferes with nighttime sleep – and the analyses conducted with a large sample lead to some interesting findings. However, this manuscript could be much improved with a clearer articulation of the study aims, and more streamlined presentation of the important results, because as it stands now, the results and discussions sections read like a laundry list of findings. Additionally, the authors should be clearer with respect to how variables were included/excluded from study.

Introduction

1.      Throughout the manuscript, the authors vacillate between discussing two aspects of “daytime sleep problems” and three aspects. For example, in the introduction, it is noted that excessive sleepiness and falling asleep in class are such sleep problems, however in table 3, there are three aspects listed (subjectively insufficient sleep, excessive sleepiness and falling asleep in class). Additionally, in the last paragraph of the discussion, only falling asleep during class is highlighted (why not the other two?). Please be consistent by always discussing the same number of aspects

2.      Please include hypotheses in your introduction.

Results

3.      It is unclear if the paragraph beginning on line 96, and starting “On weekends,” denotes that the entire paragraph is about the results from analyses of the weekends. Specifically, the sentence on line 100, “with regard to rise time…” is very unclear. Was it the author’s intention to suggest that weekday napping affects weekend rise time? Please rephrase this sentence for additional clarity.

4.      The sentence starting on line 115, “Among the answer categories…” is unclear. Please rephrase.

5.      Please define SIS, ESC, and FAC when first introduced on line 124.

Discussion

6.      To some extent, it feels like the results section in addition to the discussion section is a laundry list of findings with no clear articulation of importance of findings. For example, the sentence beginning on line 28 (“Among the attributes…”) seems to be one of the fundamental points of the study, however does not come across as important as it is buried with several other points. Ideally, this finding should be highlighted in some way. Generally, this problem may be ameliorated if the authors clearly define their hypotheses and only report on the findings that are of immediate importance to these hypotheses.

7.      The end of the second paragraph of the discussion beginning on line 190 (“Considering the circadian…”) is unclear. Please rephrase.

8.      The concepts of homeostatic sleep pressure due to experiencing some amount of slow-wave sleep is mentioned with regard to 30-min naps. It is unclear why the concept of sleep inertia is also mentioned – these two concepts are functionally distinct. Please clarify.

9.      On line 260, the authors state that FAC is “thought to be the most significant daytime sleep problems.” Please include a citation to support this statement.

Methods

10.  The authors refer to a questionnaire that covered 1) demographic variables, 2) lifestyle habits, and 3) sleep habits and sleep-related issues. Was this questionnaire validated? It seems unclear why some variables were included, while others were not. For example, why was skipping breakfast chosen as a variable of interest? The rationale for these choices should be more clearly articulated within the introduction or methods.

11.  It is similarly unclear if the “SHQ” has been validated, as the citation included does not seem to imply that it has been. Therefore, the rationale for the inclusion of the 5 sleep health factors should be more clearly defined.

12.  Other methodological choices should be better explained. For example, it is unclear why a 3 hour discrepancy between weekday and weekend sleep was chosen to define ‘oversleeper,’ or why the authors defined daytime sleep problems with three aspects, “feeling subjective insufficient sleep,” “feeling excessive sleepiness during class,” and “falling asleep during class.” If there was a specific reason these three constructs of sleepiness were chosen, it should be mentioned in the introduction/methods.

13.  Several variables were noted as ‘not applicable for the multivariate model,’ why and how were there these variables specifically excluded?

14.  The first two sentences of the first paragraph of the Materials and Methods section regarding intention to attend university seems quite important to the study rationale, therefore I encourage the authors to add these notes to the introduction.

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

the authors have responded adequately to my concerns.

Author Response

Dear Reviewer,

We sincerely appreciate your valuable comments and advices.

Koh Mizuno, PhD.

Reviewer 2 Report

I applaud the authors for this revised version as it much improved from the previous version, and significantly improves readability. The revisions to the introduction and discussion are especially well done. Unfortunately, however, this revision did introduce some minor English-language errors, which I believe can be easily addressed.

Point 1: This section is much improved! No further changes needed

Point 2: The addition of hypotheses significantly improves readability. 

Point 3:  Unfortunately, this revised sentence is equally as unclear as the previous version. Please revise again

Point 4: Similar to point 3, although the statistics are presented more clearly, the English needs to be revised - this part of the sentence "Among the answer categories of the attributes revealing significant effect on factor score of rising in the morning" is very hard to understand.

Point 5:  Point has been addressed

Point 6: This section is much improved following revision. No further changes needed.

Point 7: This point has been addressed. No further changes needed.

Point 8: Point has been addressed

Point 9: This point has been addressed. No further changes needed.

Points 10, 11, and 12: This section is much improved following revision. No further changes needed.

Point 13: This is an acceptable revision

Point 14: Point has been addressed.

Author Response

Dear Reviewer,

Thank you very much for your through review.

Regarding two points (point 3 & 4) you suggested, we revised to carefully explain the four questions asking weekdays life habits, to introduce the prominent findings, and to describe concisely. 

As we used the "Track Changes" function in Microsoft Word, please confirm revisions (line: 117-125 & 135-138). 

Again, we sincerely appreciate your valuable comments and advices.

Koh Mizuno, PhD.