Feb 23, 2018 - are provided with free text boxes to elaborate on their assessment. These free text ... Russell Pate. University of South Carolina, United States of America ... think a conclusion about improving sleeping habits/sleep quality is ... Thank you for the opportunity to review this lovely paper which focuses on ...
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ARTICLE DETAILS TITLE (PROVISIONAL)
AUTHORS
The associations between sleep quality and its domains and insufficient physical activity in a large sample of Croatian young adults: a cross-sectional study Lovro, Štefan; Sporis, Goran; Krističević, Tomislav; Knjaz, Damir
VERSION 1 – REVIEW REVIEWER REVIEW RETURNED
Russell Pate University of South Carolina, United States of America 23-Feb-2018
GENERAL COMMENTS
This study addresses an important and timely issue, and the topic is of potential interest to the readership of this journal. The basic study design and methodology, though limited in some important ways, is acceptable. In general, the manuscript is well organized and clearly written. However, there are significant concerns with certain aspects of the study and the manuscript. These include: 1. The dependent variable was a categorical expression of physical activity. While a widely used instrument was used to measure physical activity, the authors have not clearly explained how they created the physical activity categories. This should be presented in detail. 2. The instrument used to measure sleep characteristics is mislabeled. The authors refer to "sleep habits" but the appropriate term is "sleep quality." 3. The major limitation of this study is its cross-sectional design. While the authors acknowledge this, they should be much more explicit about this limitation. They hypothesize that sleep influences physical activity, but physical activity may influence sleep. They need to be much clearer on this point. Also, they need to be more careful about avoiding language that suggests causal relationships. They cannot make any claims about causal relationships. 4. They have several sentences that are way too long and difficult to read. An example is in the abstract, lines 23 to 32. Similar sentences appear elsewhere. 5. The discussion does not do an effective job of integrating these findings into the existing literature. Many relevant publications have not been considered or cited. The discussion should focus on the literature addressing associations between sleep and physical activity. Any reference to mediating mechanisms should be very carefully identified as speculative, since this study did not address any of them.
REVIEWER
Rob van Bree Open University of the Netherlands 03-Mar-2018
REVIEW RETURNED
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GENERAL COMMENTS
This manuscript reports on the cross-sectional association between sleep quality and insufficient physical activity in a very large sample of young adults. This topic is relevant. However, I have a number of concerns and suggestions that the authors should address prior to a potential publication. General - The authors use the term ‘sleeping habits’ to address ‘sleep quality’. I strongly recommend to abandon the use of ‘sleeping habits’ and to use ‘sleep quality’ throughout the manuscript. From a psychological perspective the concept of habit refers to mental efficient cue-response associations. The authors do not use ‘habit’ in their manuscript in accordance with this concept. - Please check the manuscript throughout on correct English language. Expressions such as ‘a few beneficial mechanisms’, ‘a great lifestyle changes’, and ‘each component is score from’ are incorrect. Abstract - There is a conclusion about the use of ‘special strategies and policies that leverage higher levels of physical activity’. I wonder whether this conclusion follows logically from the current study. I think a conclusion about improving sleeping habits/sleep quality is more appropriate. Strengths and limitations - Please mention the use of a cross-sectional design as a limitation of the study. Introduction - The purpose of the study is to explore the associations between sleeping habits/sleep quality and physical activity. Whereas sleeping habits/sleep quality are modelled as the independent variable, physical activity operates as the dependent variable. The introduction, however, falls short in providing a rationale for this choice. The introduction mainly describes influences of physical activity on sleep quality and, as such, seems to provide a rationale for modelling sleep quality as the dependent, but not as the independent, variable. - Please provide definitions of sufficient physical activity and/or physical inactivity. - Please provide a definition of sleeping habits/sleep quality. Materials and methods / Results - A randomization procedure with replacement was applied. Why with replacement? Does that mean that a single faculty can be selected twice? - Please change Pittsburgh Sleep Quality Questionnaire into Pittsburgh Sleep Quality Index. - Please change ‘design’ into ‘designed’. - Binge alcohol consumption is assessed using the question ‘How often do you…’. Please provide the answering options. Do I understand it correctly that answers of 1 and above are coded ‘yes’ and the answer of 0 is coded ‘no’? - Please change that α ≤ .05 into α = .05. - Why are two-sided tests applied to one-sided hypotheses? - Have the authors checked their data for multicollinearity and for outliers? Is so, they should report their efforts. If not, they should check their data.
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- Table 2 mentions odds ratios for categories within a variable. Have the authors used contrasts in their logistic regression analyses to calculate these odds ratios? If so, they should report this in the section on data analysis. Discussion - Please add a verb to the sentence ‘Although a recent metaanalytical review … small-to-medium effects [add verb] …’. Furthermore, I do not understand what the authors mean when they write about ‘moderation’. Do they mean ‘taking into account’ or do they mean ‘statistical moderation’? Please address. - The discussion suffers from the same flaw as the introduction: it mainly discusses how physical activity influences sleep quality, and not how sleep quality influences physical activity. Based on the hypotheses the latter process should be the focus of the manuscript. The authors should definitely provide more theoretical foundation and discussion of the way sleep quality is related to physical activity. In the current form the manuscript falls short on this point. - Please address the extent to which the findings of the current study can be generalized to other populations. - Please address directions for future research. - The authors mention that they have set a hypothesis for the influence of psychological distress. However, this hypothesis is nowhere mentioned in the methods section. This section only describes psychological distress as a variable that is accounted for. Please address. - The final conclusion that the findings of the current study should be taken into account when establishing and implementing special strategies that enhance sleep quality and higher participation in physical activity does not follow logically from this study. The conclusion that enhancing sleep quality may be important in light of improving physical activity levels seems more appropriate. REVIEWER
REVIEW RETURNED GENERAL COMMENTS
Xiaolin Yang, PhD, Adjunct Professor LIKES Research Centre for Physical Activity and Health, Jyväskylä, Finland 05-Mar-2018 MS ID: bmjopen-2018-021902 Title: The associations between sleeping habits and insufficient physical activity in a large sample of young adults Thank you for the opportunity to review this lovely paper which focuses on whether sleeping habits are related to insufficient physical activity among a large sample of Croatian university students. Overall, I think the paper has the potential to contribute significantly to the field. I do, however, have a few suggestions for the authors to improve this paper, and these are presented below. Abstract Page 2 line 8. I suggest using the words ‘insufficient physical activity’ instead of ‘physical activity’ because of the propose of this study. Page 2 line 23. In the abstract results, it would be useful to state in which direction the associations are from separate analyses on unadjusted and adjusted findings and it would be preferable to provide some numeric results. Page 2 line 27. ‘shorter sleep duration’ should be deleted because
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the words are repeated. Throughout the paper the double quotation marks that are used to enclose quoted sufficiently active and insufficiently active should be omitted. Strengths and limitations of the study Page 3 line 10. I am not sure that the words ‘sleep complaints’ is correct here – maybe replace with ‘poor sleep quality’. Introduction Page 4 line 6. The first paragraph of the introduction needs to be made more explicit. The authors introduce physical inactivity as one of the leading risk factors for disease burden and mental diseases. I suggest defining insufficient physical activity at the outset and how it is operationalized in the existing research. Page 4 line 15. The second paragraph, poor sleep quality is a wellknown traditional risk factor for poor health-related quality of life, which is generally considered to be non-modifiable for obvious reasons. The link between sleep habits and physical inactivity needs consideration for the initial logic to make sense. Answer: Why are sleep habits important? Do unhealthy sleep habits contribute to physical inactivity? What are socio-demographic, health-related and psychological variables associated with sleep habits and physical activity in the young adult population. Is there a mechanism to underlie the relation between unhealthy sleep habits and physical inactivity? Therefore, I would like the authors to consider the contribution to knowledge and understanding that is being made by this work and contain explicit details of hypothesis in the text because it is a lack of theoretical framework. Page 4 line 41. In the third paragraph, the description of sleep and lifestyle changes in young adults is generally well done, but I think the authors have a chance to broaden the importance of their current study here. It has been recommended more generally to utilize the large data sets to examine gender differences in the relationship between sleep habits and physical activity in young adults. Differences in sleep behavior and sleep disorders may not only be driven by physical activity but also by gender differences. These differences may be mediated by socio-demographic, healthrelated and psychological variables. The current work is one of the most robust tests of this suggestion. Materials and Methods Please describe when the data have been measured. It is acceptable to use multivariate regression analyses as long as all statistical assumptions are met; however, given the numbers of parameters, the critical level of significance should be adjusted accordingly. The research incorporates a large sample, but I would like to know why gender-specific patterns have not been presented. Results A descriptive table about who the participants are would be very useful. This should include all covariates, stratified by gender.
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Correlations should be used to examine the correlations between all variables in another table. The work may help explain why the covariate adjustment is required for sound statistical analysis. Percentage of Table 1 should be clarified. In particular, the proportion of sleep quality is incorrect. In Table 1, it is not necessary to describe the empty cells in the variable of sleep duration. Page 8 lines 35-44. These sentences should be rephrased because of repeated words. I suggest simply writing that ‘In multivariate model, these associations remained significant after adjustment for……, with the exception of sleep disturbances’. Discussion Page 8 line 48. In the first paragraph, the findings of the study should be slightly rephrased. Page 9 line 7. In the second paragraph, I would expect the authors to strength the discussion concerning the effects of poor sleep habits on insufficient physical activity within the context of published literature. For example, previous studies found that adults with poor sleep were less likely to be physically active than adults without sleep complaints. Furthermore, there is very little evidence to support the mechanisms and this section should be revised to focus more on the data presented. The results showed that the relationship between sleep disturbances and physical inactivity disappeared after adjustment for all covariates. A critical discussion of the result is required. Given the large sample size, the results should be interpreted by effect size as well as p level. Also, I think the multivariate regression method analyzing sleeping habits with physical inactivity (stratified by gender) would be of interest to readers in addition to the analyses presented.
VERSION 1 – AUTHOR RESPONSE Dear Editor, We really thank you and appreciate that you consider our manuscript to be published in your Journal after major modifications. We also want to thank for the opportunity to revise the manuscript according to reviewer’s comments and suggestions. Second, we are very thankful to reviewers, who pointed out some comments and suggestions to improve our manuscript. Reviewer: 1 Reviewer Name: Russell Pate Institution and Country: University of South Carolina, United States of America Please state any competing interests or state ‘None declared’: No conflicts
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Please leave your comments for the authors below This study addresses an important and timely issue, and the topic is of potential interest to the readership of this journal. The basic study design and methodology, though limited in some important ways, is acceptable. In general, the manuscript is well organized and clearly written. However, there are significant concerns with certain aspects of the study and the manuscript. These include: 1. The dependent variable was a categorical expression of physical activity. While a widely used instrument was used to measure physical activity, the authors have not clearly explained how they created the physical activity categories. This should be presented in detail. Comment: Accepted. We enriched the “Materials and Methods” section (the “outcome variable” sub-section) and clearly described how we created the physical activity categories. “To assess physical activity in the last 7 days, we used International Physical Activity questionnaire, a reliable and valid instrument designed to measure physical activity in respondents between ages 18-65 [9]. It provided information about the time and number of days spent walking, in moderate and vigorous intensity physical activity. For each participant, we calculated the time spent in moderate and vigorous physical activity. According to the World Health Organization [3], ‘sufficient’ physical activity is defined as doing at least (1) 150 min/week of moderate physical activity or (2) 75 min/week of vigorous physical activity or (3) an equivalent combination of both. Thus, we categorized the participants who met the aforementioned recommendation as ‘sufficiently’ active compared with the participants who did not meet the recommended levels of physical activity weekly.” 2. The instrument used to measure sleep characteristics is mis-labeled. The authors refer to "sleep habits" but the appropriate term is "sleep quality." Comment: Accepted. We deleted the term “sleep habits” and replaced it with “sleep quality” in the “Data analysis” section.
3. The major limitation of this study is its cross-sectional design. While the authors acknowledge this, they should be much more explicit about this limitation. They hypothesize that sleep influences physical activity, but physical activity may influence sleep. They need to be much clearer on this point. Also, they need to be more careful about avoiding language that suggests causal relationships. They cannot make any claims about causal relationships. Comment: Accepted. We rewrote the “Limitation” section and stated, that previous studies (Lang et al., 2015; Gerber et al., 2010; Chennaoui et al., 2015; Brand et al., 2014) have also examined and confirmed the reverse association, that is, physical activity is associated with sleeping patterns. However, based on our study design, the direction of the association remained unclear. 1. Brand S, Kalak N, Gerber M, Kirov R, Puhse U, Holsboer-Trachsler E: High selfperceived exercise exertion before bedtime is associated with greater objectively assessed sleep efficiency. Sleep Med 2014;15:1031-1036. 2. Gerber M, Brand S, Holsboer-Trachsler E, Puhse U: Fitness and exercise as correlates of sleep complaints: is it all in our minds? Medicine and science in sports and exercise 2010;42:893-901. 3. Lang C, Kalak N, Brand S, Holsboer-Trachsler E, Puhse U, Gerber M: The relationship between physical activity and sleep from mid adolescence to early adulthood. A systematic review of methodological approaches and meta-analysis. Sleep medicine reviews 2016;28:32-45. 4. Chennaoui M, Arnal PJ, Sauvet F, Leger D: Sleep and exercise: a reciprocal issue? Sleep medicine reviews 2015;20:59-72.
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4. They have several sentences that are way too long and difficult to read. An example is in the abstract, lines 23 to 32. Similar sentences appear elsewhere. Comment: Accepted. We rewrote the aforementioned sentences in lines 23 to 32 and still looked throughout the text to keep possibly large sentences much clearer. 5. The discussion does not do an effective job of integrating these findings into the existing literature. Many relevant publications have not been considered or cited. The discussion should focus on the literature addressing associations between sleep and physical activity. Any reference to mediating mechanisms should be very carefully identified as speculative, since this study did not address any of them. Comment: Accepted. We enriched the “Discussion” section with previous studies aiming to explore the associations between sleep quality and physical activity.
Reviewer: 2 Reviewer Name: Rob van Bree Institution and Country: Open University of the Netherlands Please state any competing interests or state ‘None declared’: None declared Please leave your comments for the authors below This manuscript reports on the cross-sectional association between sleep quality and insufficient physical activity in a very large sample of young adults. This topic is relevant. However, I have a number of concerns and suggestions that the authors should address prior to a potential publication. General The authors use the term ‘sleeping habits’ to address ‘sleep quality’. I strongly recommend to abandon the use of ‘sleeping habits’ and to use ‘sleep quality’ throughout the manuscript. From a psychological perspective the concept of habit refers to mental efficient cue-response associations. The authors do not use ‘habit’ in their manuscript in accordance with this concept. Comment: Accepted. We deleted the term ‘sleeping habits’ and replaced it with ‘sleep quality’ throughout the manuscript. Please check the manuscript throughout on correct English language. Expressions such as ‘a few beneficial mechanisms’, ‘a great lifestyle changes’, and ‘each component is score from’ are incorrect. Comment: Accepted. We looked throughout the whole manuscript and corrected the aforementioned phrases. Abstract There is a conclusion about the use of ‘special strategies and policies that leverage higher levels of physical activity’. I wonder whether this conclusion follows logically from the current study. I think a conclusion about improving sleeping habits/sleep quality is more appropriate. Comment: Accepted. We reformulated the ‘Conclusion’ section and stated that special strategies and policies that leverage good sleep quality are warranted.
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Strengths and limitations Please mention the use of a cross-sectional design as a limitation of the study. Comment: Accepted. We enriched the ‘Strengths and limitations’ section with using a crosssectional design. Introduction The purpose of the study is to explore the associations between sleeping habits/sleep quality and physical activity. Whereas sleeping habits/sleep quality are modelled as the independent variable, physical activity operates as the dependent variable. The introduction, however, falls short in providing a rationale for this choice. The introduction mainly describes influences of physical activity on sleep quality and, as such, seems to provide a rationale for modelling sleep quality as the dependent, but not as the independent, variable. Please provide definitions of sufficient physical activity and/or physical inactivity. Please provide a definition of sleeping habits/sleep quality. Comment: Accepted. We rewrote the whole ‘Introduction’ section and provided additional information about the association between sleep quality domains with physical activity. We also stated the definition of physical activity and sleep quality. Materials and methods / Results A randomization procedure with replacement was applied. Why with replacement? Does that mean that a single faculty can be selected twice? Comment: Explained. Each faculty had a unique code on a slip of paper and was randomly drawn from the box. When the faculty was selected, the code was put back in the box, so again other faculties had the same opportunity to get selected. -
Please change Pittsburgh Sleep Quality Questionnaire into Pittsburgh Sleep Quality Index.
Comment: Accepted. We changed ‘Pittsburgh Sleep Quality Questionnaire’ into ‘Pittsburgh Sleep Quality Index’ -
Please change ‘design’ into ‘designed’.
Comment: Accepted. We changed ‘design’ into ‘designed’. Binge alcohol consumption is assessed using the question ‘How often do you…’. Please provide the answering options. Do I understand it correctly that answers of 1 and above are coded ‘yes’ and the answer of 0 is coded ‘no’? Comment: Explained. Participants reported the answer in numerical way (1,2,3,4....) and then, we looked specifically how many drinks do men and women occasionally drink during on one occasion. Then, if men or women had more then 4 and 5 drinks on one occasion were coded with 1 and those who did not were coded with 0. -
Please change that α ≤ .05 into α = .05.
Comment: Accepted. We changed α ≤ .05 into α = .05. -
Why are two-sided tests applied to one-sided hypotheses?
Comment: Accepted. We performed the analysis with 1-sided value, but accidentally wrote that it was 2-sided.
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Have the authors checked their data for multicollinearity and for outliers? Is so, they should report their efforts. If not, they should check their data. Comment: Accepted. We additionally checked for multicollinearity by using variance inflation factors and for outliers. “We tested the data for multicollinearity using the variance inflation factors, normality of residuals using the normal probability plot and histogram of residuals; and 3) heteroscedasticity using the standardized residuals vs. predicted plot. The variance inflation factors in our model ranged between 1.01 and 1.85 indicating no multicollinearity and the other assumptions were also met.” Table 2 mentions odds ratios for categories within a variable. Have the authors used contrasts in their logistic regression analyses to calculate these odds ratios? If so, they should report this in the section on data analysis. Comment: Accepted. Correct, we used contrasts in logistic regression analyses to calculate odds ratios. Thus, we reported that in our “Data analysis” section. Discussion Please add a verb to the sentence ‘Although a recent meta-analytical review … small-to-medium effects [add verb] …’. Furthermore, I do not understand what the authors mean when they write about ‘moderation’. Do they mean ‘taking into account’ or do they mean ‘statistical moderation’? Please address. Comment: Accepted. We deleted the aforementioned sentence, since we are not talking about moderation. The discussion suffers from the same flaw as the introduction: it mainly discusses how physical activity influences sleep quality, and not how sleep quality influences physical activity. Based on the hypotheses the latter process should be the focus of the manuscript. The authors should definitely provide more theoretical foundation and discussion of the way sleep quality is related to physical activity. In the current form the manuscript falls short on this point. Comment: Accepted. As for the other reviewers, we changed our “Discussion” method and clearly stated about the association between sleep quality domains and sleep quality in general and physical activity. Please address the extent to which the findings of the current study can be generalized to other populations. Comment: Accepted. We stated that we used a university student’s sample that cannot be a representative sample for young adults elsewhere. -
Please address directions for future research.
Comment: Accepted. We added at the end of the “Limitation” section the future direction. The authors mention that they have set a hypothesis for the influence of psychological distress. However, this hypothesis is nowhere mentioned in the methods section. This section only describes psychological distress as a variable that is accounted for. Please address. Comment: Accepted. We think that it would be better to delete this part. Although we accounted for psychological distress, we did not perform ‘mediation’ effect and cannot establish whether psychological distress played a mediating role between sleep quality domains and sleep quality in general and physical activity.
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The final conclusion that the findings of the current study should be taken into account when establishing and implementing special strategies that enhance sleep quality and higher participation in physical activity does not follow logically from this study. The conclusion that enhancing sleep quality may be important in light of improving physical activity levels seems more appropriate. Comment: Accepted. We are now aware that we based our conclusion on different association (that physical activity has on sleep quality) but not vice versa. Thus, we rewrote the “Conclusion” section. Reviewer 3 MS ID: bmjopen-2018-021902 Title: The associations between sleeping habits and insufficient physical activity in a large sample of young adults Thank you for the opportunity to review this lovely paper which focuses on whether sleeping habits are related to insufficient physical activity among a large sample of Croatian university students. Overall, I think the paper has the potential to contribute significantly to the field. I do, however, have a few suggestions for the authors to improve this paper, and these are presented below. Abstract Page 2 line 8. I suggest using the words ‘insufficient physical activity’ instead of ‘physical activity’ because of the propose of this study. Comment: Accepted. We used the word ‘insufficient’ physical activity. Page 2 line 23. In the abstract results, it would be useful to state in which direction the associations are from separate analyses on unadjusted and adjusted findings and it would be preferable to provide some numeric results. Comment: Accepted. We added numeric results and stated in which direction the associations went. Page 2 line 27. ‘shorter sleep duration’ should be deleted because the words are repeated. Throughout the paper the double quotation marks that are used to enclose quoted sufficiently active and insufficiently active should be omitted. Comment: Accepted. We removed the double quotation marks throughout the manuscript. Strengths and limitations of the study Page 3 line 10. I am not sure that the words ‘sleep complaints’ is correct here – maybe replace with ‘poor sleep quality’. Comment: Accepted. Introduction Page 4 line 6. The first paragraph of the introduction needs to be made more explicit. The authors introduce physical inactivity as one of the leading risk factors for disease burden and mental diseases. I suggest defining insufficient physical activity at the outset and how it is operationalized in the existing research. Comment: Accepted. We clarified physical inactivity. Page 4 line 15. The second paragraph, poor sleep quality is a well-known traditional risk factor for poor health-related quality of life, which is generally considered to be non-modifiable for obvious reasons. The link between sleep habits and physical inactivity needs consideration for the initial logic to make sense. Answer: Why are sleep habits important? Do unhealthy sleep habits contribute to physical inactivity? What are socio-demographic, health-related and psychological variables associated with sleep habits and physical activity in the young adult population. Is there a mechanism to underlie the relation between unhealthy sleep habits and physical inactivity? Therefore, I would like the authors to consider the contribution to knowledge and understanding that is being made by this work and contain explicit details of hypothesis in the text because it is a lack of theoretical framework. Comment: Accepted. We clarified what sleep quality is and incorporated the existing studies aiming to investigate the associations between sleep quality and physical activity. We are aware that we wrote about the association between physical activity and sleep quality, which is not the theme of this study. Page 4 line 41. In the third paragraph, the description of sleep and lifestyle changes in young adults is generally well done, but I think the authors have a chance to broaden the importance of their
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current study here. It has been recommended more generally to utilize the large data sets to examine gender differences in the relationship between sleep habits and physical activity in young adults. Differences in sleep behavior and sleep disorders may not only be driven by physical activity but also by gender differences. These differences may be mediated by socio-demographic, healthrelated and psychological variables. The current work is one of the most robust tests of this suggestion. Comment: Accepted. We enriched the paragraph by providing the information about gender differences in sleep quality and which factors (socio-demographic, lifestyle/health-related) are associated with sleep quality and physical activity. Materials and Methods Please describe when the data have been measured. Comment: Accepted. It is acceptable to use multivariate regression analyses as long as all statistical assumptions are met; however, given the numbers of parameters, the critical level of significance should be adjusted accordingly. The research incorporates a large sample, but I would like to know why genderspecific patterns have not been presented. Comment: Explained. We calculated the interaction effect in all sleep quality domains an in general sleep quality and found no statistically significant effect (p-value ranged between 0.120.45), so we dropped the gender-specific analyses in the association between sleep quality domains and sleep quality in general and physical activity. Results A descriptive table about who the participants are would be very useful. This should include all covariates, stratified by gender. Comment: Accepted. We deleted the table stratified by physical activity and included a new table stratified by gender and all covariates. Correlations should be used to examine the correlations between all variables in another table. The work may help explain why the covariate adjustment is required for sound statistical analysis. Comment: Accepted. We created a table with correlation coefficients between all variables. Percentage of Table 1 should be clarified. In particular, the proportion of sleep quality is incorrect. In Table 1, it is not necessary to describe the empty cells in the variable of sleep duration. Comment: Accepted. As we stated before, we created a new table stratified by gender and recalculated the proportions. Page 8 lines 35-44. These sentences should be rephrased because of repeated words. I suggest simply writing that ‘In multivariate model, these associations remained significant after adjustment for……, with the exception of sleep disturbances’. Comment: Accepted. We rewrote the sentence. Discussion Page 8 line 48. In the first paragraph, the findings of the study should be slightly rephrased. Comment: Accepted. We slightly reformulated the sentence. Page 9 line 7. In the second paragraph, I would expect the authors to strength the discussion concerning the effects of poor sleep habits on insufficient physical activity within the context of published literature. For example, previous studies found that adults with poor sleep were less likely to be physically active than adults without sleep complaints. Furthermore, there is very little evidence to support the mechanisms and this section should be revised to focus more on the data presented. Comment: Accepted. We specifically focused on the associations between sleep quality with physical activity and not vice versa and enriched the “Discussion” section. The results showed that the relationship between sleep disturbances and physical inactivity disappeared after adjustment for all covariates. A critical discussion of the result is required. Comment: Accepted. Given the large sample size, the results should be interpreted by effect size as well as p level. Also, I think the multivariate regression method analyzing sleeping habits with physical inactivity (stratified by gender) would be of interest to readers in addition to the analyses presented. Comment: Explained. We think that the results should be interpreted as we already did, since in general, large epidemiological studies report (if they perform logistic regression analysis) odds ratios with 95% confidence intervals and p level of significance. Also, we calculated the interaction between gender and sleeping habits/patterns/sleep quality domains and found no significant effect, so we dropped the gender-specific analyses.
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VERSION 2 – REVIEW REVIEWER REVIEW RETURNED
Xiaolin Yang, PhD, Adjunct Professor LIKES Research Centre for Physical Activity and Health, Finland 23-Mar-2018
GENERAL COMMENTS
The paper is well presented and written. The authors have done a good work with my suggestions. I'd appreciate it if the manuscript is accepted.
REVIEWER
Rob van Bree Open University of the Netherlands 25-Mar-2018
REVIEW RETURNED GENERAL COMMENTS
I commend the authors for their thorough revision of their manuscript. The manuscript has improved substantially. Nevertheless, I have some concerns and suggestions that the authors should address prior to a potential publication. Title - I do not understand why the authors refer to ‘sleeping patterns’ in the title of their manuscript, whereas they refer to ‘sleep quality’ in their manuscript. The most appropriate term seems to be ‘sleep quality’. Please use that term in the title. - In general, please check the manuscript throughout for the consistent use of the term ‘sleep quality’. The authors use ‘sleep quality’, ‘sleep problems’, and ‘sleep patterns’ interchangeably. For reasons of clarity, please use ‘sleep quality’ throughout. Abstract - The authors describe the objective of their study as exploring associations between sleep quality and insufficient physical activity. However, they are not consistent in this aim. In line 12 in the abstract, as well as in other places throughout their manuscript, they describe their aim as exploring associations between sleep quality and physical activity, without the adjective ‘insufficient’. Please check the manuscript throughout on a consistent presentation of the aim of the study. - The authors should also mention socioeconomic status as a control variable. Introduction - Where does ‘anxiety’ comes from in the sentence ‘… pointing out that the higher prevalence of anxiety among women alone cannot explain the gender differences in sleep disturbances’? Please explain or delete. - At the end of the introduction the authors use the term ‘sleeping habits’. Please correct. Materials and methods - Even after the authors’ reply on this point, I still do not understand why a randomization procedure with replacement was applied. I suggest deleting the sentence that mentions this procedure. - The authors now describe that they operationalized physical activity as the time and number of days spent walking, in moderate and vigorous intensity. However, physical activity consists of a lot more than only walking. If the authors mistakenly mentioned ‘walking’, they should correct this error. If they truly operationalized physical activity as walking, they should replace ‘physical activity’ by
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‘walking’ throughout their manuscript, including the title. Data analysis - Please delete ‘3)’. - All the analysis = All the analyses. Table 1 - Table 1 now presents the characteristics of the study participants stratified by gender. The table no longer presents the characteristics stratified by level of physical activity, which was informative in the previous version of this manuscript. I would suggest to present the characteristics stratified both by gender and by physical activity. Discussion - In the first paragraph of the discussion the use of the terms ‘increased’, ‘fragmented’, and ‘excessive use’ do not seem justified. Term such as ‘higher’, ‘shorter’, and ‘use’ seem more appropriate. Please also check the remainder of the discussion for the incorrect use of these terms. - ‘However, the lack of significant association between sleep disturbances and physical activity could be explained by using subjective methods to assess the level of physical activity and sleep disturbances’. Please explain. Conclusions - Although I understand what the authors aim to say, the last sentence of this paragraph is grammatically incorrect. Please address.
VERSION 2 – AUTHOR RESPONSE Reviewer: 3 Reviewer Name: Xiaolin Yang, PhD, Adjunct Professor
Institution and Country: LIKES Research Centre for Physical Activity and Health, Finland
Please state any competing interests or state ‘None declared’: None declared.
Please leave your comments for the authors below The paper is well presented and written. The authors have done a good work with my suggestions. I'd appreciate it if the manuscript is accepted. Comment: Thank you very much for your valuable comments and suggestions for improving our manuscript and the opportunity to publish it in BMJ Open. We are glad that we took care everything you told us to do.
Reviewer: 2 Reviewer Name: Rob van Bree
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Institution and Country: Open University of the Netherlands
Please state any competing interests or state ‘None declared’: None declared
Please leave your comments for the authors below I commend the authors for their thorough revision of their manuscript. The manuscript has improved substantially. Nevertheless, I have some concerns and suggestions that the authors should address prior to a potential publication.
Title - I do not understand why the authors refer to ‘sleeping patterns’ in the title of their manuscript, whereas they refer to ‘sleep quality’ in their manuscript. The most appropriate term seems to be ‘sleep quality’. Please use that term in the title. Comment: Accepted. We added ‘sleep quality’ instead of ‘sleeping patterns’. However, we also took into account ‘sleep quality domains’ (subjective sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, use of sleep medication and daytime dysfunction), so we believe that along with ‘sleep quality’, in the ‘Title’ should be also stated ‘sleep quality and its domains’. - In general, please check the manuscript throughout for the consistent use of the term ‘sleep quality’. The authors use ‘sleep quality’, ‘sleep problems’, and ‘sleep patterns’ interchangeably. For reasons of clarity, please use ‘sleep quality’ throughout. Comment: Accepted. We replace the terms ‘sleep problems and sleep patterns’ with the term ‘sleep quality’.
Abstract - The authors describe the objective of their study as exploring associations between sleep quality and insufficient physical activity. However, they are not consistent in this aim. In line 12 in the abstract, as well as in other places throughout their manuscript, they describe their aim as exploring associations between sleep quality and physical activity, without the adjective ‘insufficient’. Please check the manuscript throughout on a consistent presentation of the aim of the study. Comment: Accepted. We added the adjective ‘insufficient’ throughout the manuscript. - The authors should also mention socioeconomic status as a control variable. Comment: Accepted. We added ‘socioeconomic status’.
Introduction
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- Where does ‘anxiety’ comes from in the sentence ‘… pointing out that the higher prevalence of anxiety among women alone cannot explain the gender differences in sleep disturbances’? Please explain or delete. Comment: Accepted. We deleted the aforementioned part of the sentence. - At the end of the introduction the authors use the term ‘sleeping habits’. Please correct. Comment: Accepted. We corrected the term and used the term ‘sleep quality’ throughout the manuscript.
Materials and methods - Even after the authors’ reply on this point, I still do not understand why a randomization procedure with replacement was applied. I suggest deleting the sentence that mentions this procedure. Comment: Accepted. We deleted the sentence. - The authors now describe that they operationalized physical activity as the time and number of days spent walking, in moderate and vigorous intensity. However, physical activity consists of a lot more than only walking. If the authors mistakenly mentioned ‘walking’, they should correct this error. If they truly operationalized physical activity as walking, they should replace ‘physical activity’ by ‘walking’ throughout their manuscript, including the title. Comment: Accepted. We stated that physical activity was assessed via the number of days and time spent in light, moderate and vigorous physical activity.
Data analysis - Please delete ‘3)’. - All the analysis = All the analyses. Comment: Accepted. We corrected the aforementioned suggestions.
Table 1 - Table 1 now presents the characteristics of the study participants stratified by gender. The table no longer presents the characteristics stratified by level of physical activity, which was informative in the previous version of this manuscript. I would suggest to present the characteristics stratified both by gender and by physical activity. Comment: Accepted. We added the table from the previous version of the manuscript showing the prevalence of sleeping characteristics according to the level of physical activity as Table 2 in the new manuscript.
Discussion
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- In the first paragraph of the discussion the use of the terms ‘increased’, ‘fragmented’, and ‘excessive use’ do not seem justified. Term such as ‘higher’, ‘shorter’, and ‘use’ seem more appropriate. Please also check the remainder of the discussion for the incorrect use of these terms. Comment: Accepted. We changed the terms ‘increased’, ‘fragmented’ and ‘excessive use’ with ‘higher’, ‘shorter’ and ‘use’. - ‘However, the lack of significant association between sleep disturbances and physical activity could be explained by using subjective methods to assess the level of physical activity and sleep disturbances’. Please explain. Comment: Accepted. We stated in the ‘Discussion’ section that by using self-reports might have led to different perception of the level of physical activity or sleep quality and could have also led to overall method bias.
Conclusions - Although I understand what the authors aim to say, the last sentence of this paragraph is grammatically incorrect. Please address. Comment: Accepted. We corrected the last sentence of the ‘Conclusion’ paragraph.
VERSION 3 – REVIEW REVIEWER REVIEW RETURNED GENERAL COMMENTS
Rob van Bree Open University of the Netherlands 30-Apr-2018 Once again I commend the authors for their revision of their manuscript. I consider that all the concerns that I raised were treated in the manuscript. In the previous round of reviews I wrote that “in the first paragraph of the discussion the use of the terms ‘increased’, ‘fragmented’, and ‘excessive use’ do not seem justified. Term such as ‘higher’, ‘shorter’, and ‘use’ seem more appropriate”. Although the authors changed these expressions in the discussion section, they did not do so in the last paragraph of the results section. I suggest that the authors address this comment in their final version. That version will, as far as I am concerned, be suitable for publication, albeit with the reservation mentioned below. A final remark concerns the addition of a fourth author. It is not very common to add authors at this stage of the review process and to declare in the ‘author contributions’ that this newly added author, in cooperation with the other authors, ‘conceived this study, wrote this manuscript and analyzed the data’. In the rebuttal letter the authors do not explain why this author was added. I leave it up to the discretion of the editor to decide on this topic.
VERSION 3 – AUTHOR RESPONSE Reviewer(s)' Comments to Author:
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Reviewer: 2 Reviewer Name: Rob van Bree Institution and Country: Open University of the Netherlands Please state any competing interests or state ‘None declared’: Non declared Please leave your comments for the authors below Once again I commend the authors for their revision of their manuscript. I consider that all the concerns that I raised were treated in the manuscript. In the previous round of reviews I wrote that “in the first paragraph of the discussion the use of the terms ‘increased’, ‘fragmented’, and ‘excessive use’ do not seem justified. Term such as ‘higher’, ‘shorter’, and ‘use’ seem more appropriate”. Although the authors changed these expressions in the discussion section, they did not do so in the last paragraph of the results section. I suggest that the authors address this comment in their final version. That version will, as far as I am concerned, be suitable for publication, albeit with the reservation mentioned below. Comment: Accepted. We also did changes in the ‘Results’ section and replaced the use of the terms ‘increased’, ‘fragmented’, and ‘excessive use’ with terms ‘higher’, ‘shorter’, and ‘use’. A final remark concerns the addition of a fourth author. It is not very common to add authors at this stage of the review process and to declare in the ‘author contributions’ that this newly added author, in cooperation with the other authors, ‘conceived this study, wrote this manuscript and analyzed the data’. In the rebuttal letter the authors do not explain why this author was added. I leave it up to the discretion of the editor to decide on this topic. Comment: Explained. We included prof. Damir Knjaz as co-author, due to his expertise in correlation analysis (one of the reviewers has told that we should perform a correlation analysis between all the variables) and he also helped to interpret the results. We did not include this authors previously, because he only conceived the study at the beginning and in the final round of the revision, he helped with data analysis and interpretation.
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