PEER REVIEW HISTORY BMJ Open Publishes All Reviews Undertaken
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BMJ Open: first published as 10.1136/bmjopen-2014-006983 on 15 June 2015. Downloaded from PEER REVIEW HISTORY BMJ Open publishes all reviews undertaken for accepted manuscripts. Reviewers are asked to complete a checklist review form (http://bmjopen.bmj.com/site/about/resources/checklist.pdf) and are provided with free text boxes to elaborate on their assessment. These free text comments are reproduced below. ARTICLE DETAILS TITLE (PROVISIONAL) The association between body height and chronic low back pain: a follow-up in the Nord-Trøndelag Health Study AUTHORS Heuch, Ingrid; Heuch, Ivar; Hagen, Knut; Zwart, John-Anker VERSION 1 - REVIEW REVIEWER Alexis Descatha Versailles University, Paris Hospital, Inserm REVIEW RETURNED 23-Feb-2015 GENERAL COMMENTS The author to study association between body height and chronic low back pain (LBP, 3month of back pain) in a large cohort ( 3883 women and 2662 men with LBP, and 10 059 women and 8725 men without LBP), after 11 years. Small but significant association was found only for women: a higher risk of LBP was demonstrated for height ≥170 cm, after adjustment for other risk factors (relative risk 1.19, 95% confidence interval 1.03 to 1.37; compared to height <160 cm). Interesting, I have some comments about methods, results and discussion. http://bmjopen.bmj.com/ 1. One major comment is about the reference used. I feel authors must consider the average height for men and women as the reference and not the lowest height. For men it is from180-184 cm and women 165-169 cm in Scandinavia (Garcia, Jaume, et Climent Quintana-Domeque. « The Evolution of Adult Height in Europe: A Brief Note ». Economics and Human Biology 5, no 2 (juillet 2007): 340 349. doi:10.1016/j.ehb.2007.02.002.) I am not sure conclusions are still valid with such comparison. on October 2, 2021 by guest. Protected copyright. Methods 2. Details on how were assess the variable used for adjusting are essential to be given (physical activity self reported? Job exposure matrix?) Results 3. A flow chart must be given since there is attrition. Comparison of followed subjects vs not followed must be detailed in a table. 4. Distribution of adjusting variables should be described in the sample (table). Discussion 5. Medical history of low back pain, trauma, spondylarthropathy should be discuss (if not available), like access of care/surgery. 6. The consequences of the finding must be discussed = what are the consequences for practitioner and for the researcher, considering the excess of risk is small …. BMJ Open: first published as 10.1136/bmjopen-2014-006983 on 15 June 2015. Downloaded from Minor I am not clear about the choice of the GLM with a log link instead of the use of logistic model REVIEWER Frits Oosterveld Saxion University School of Health The Netherlands REVIEW RETURNED 08-Apr-2015 GENERAL COMMENTS From a research perspective the association between body height and LBP is an interesting question, but clinical relevance is lacking. if taller people have a higher risk for developing LBP there still are no therapeutic or preventive options to reduce that risk. Although the scientific evidence from literature is minimal or conflicting, the relevance for the analysis in this study is still small. It seems that only a combination of high BMI (>30) and higher body height has clinical relevance, RR 1.13 and 1.17 respectively for women and man, although statistical significance is absent. So clinicians should be alert on over weighted tall people in the prevention of LBP and advise them to lose weight. The summary of literature in the discussion seems to prove the positive relation between body height and LBP incidence, but no figures are mentioned. Statistical significance is easily reached in such large cohort studies, but the magnitude of the risk may be clinically irrelevant, so the effect can overestimated. This study has its value in the proof of a very small association http://bmjopen.bmj.com/ between body height and LBP, that is clinically irrelevant and cannot be influenced by treatment! The reviewer also provided a marked copy with detailed comments. Please contact the publisher for full information about it. VERSION 1 – AUTHOR RESPONSE on October 2, 2021 by guest. Protected copyright. Reviewer no. 1 (Descatha) Reviewer's remark: Interesting, I have some comments about methods, results and discussion. 1. One major comment is about the reference used. I feel authors must consider the average height for men and women as the reference and not the lowest height. For men it is from180-184 cm and women 165-169 cm in Scandinavia (Garcia, Jaume, et Climent Quintana-Domeque. « The Evolution of Adult Height in Europe: A Brief Note ». Economics and Human Biology 5, no 2 (juillet 2007): 340 349. doi:10.1016/j.ehb.2007.02.002.) I am not sure conclusions are still valid with such comparison. Our response: We agree that it is important to compare the risk for an extreme value of a risk factor with the BMJ Open: first published as 10.1136/bmjopen-2014-006983 on 15 June 2015. Downloaded from corresponding risk associated with a typical population value. For a basically continuous risk factor such as body height, we feel this is achieved in a better way by considering estimates based on the original exact measurements, rather than relying on a discrete categorization. We have therefore taken up the suggestion of the reviewer and we have added a comparison of this kind at the end of the first paragraph in the discussion, using the average height for women determined in the population under study. It seems to us that this gives a better impression of the magnitude of the associations involved than what may be achieved by changing the reference group in the categorical analysis. The 5 cm intervals considered are really too wide to represent the average height in a meaningful way. In any case, the statistical significance of the association between height and LBP would not be affected by a different choice of reference category. Also, with the four categories of height considered here, designating one of the internal categories as a reference category would introduce an unwanted asymmetry in the display of risks, as it is not possible to pick out an exact middle category. It is common practice in epidemiology to use the lowest interval as the reference category, provided that it is large enough to give stable estimates (which is the case here). The point raised by the reviewer is more easily illustrated considering height as a continuous variable, and we have thus retained the original reference group in the categorical analysis. Reviewer's remark: Methods 2. Details on how were assess the variable used for adjusting are essential to be given (physical activity self reported? Job exposure matrix?) Our response: It is correct that our original manuscript did not describe in detail how the information was collected on covariates used for adjustment. We have now added three new paragraphs to the "Exposure and http://bmjopen.bmj.com/ covariate assessment" part of the methods section to explain the data collection and the use of categories for each covariate. In particular, it is specified how the levels of physical activity in leisure time were defined, essentially on the basis of self-reported information about the number of hours spent each week on light and hard activities. For the questions concerning job activities, the respondents were presented with alternative categories exemplified by specific job descriptions. These examples are now briefly described in the manuscript. on October 2, 2021 by guest. Protected copyright. Reviewer's remark: Results 3. A flow chart must be given since there is attrition. Comparison of followed subjects vs not followed must be detailed in a table. Our response: We have now added a figure with a flow-chart, indicating how participants were lost or excluded at different stages of our study. At the same time, the chart explains how the groups arose that were included in the statistical analysis at the end of the prospective study among those with and without LBP at baseline. Because of this addition, the corresponding text in the methods section has been slightly modified. BMJ Open: first published as 10.1136/bmjopen-2014-006983 on 15 June 2015. Downloaded from Furthermore, we have now included four new supplementary tables describing the distribution of variables in the cohort of respondents without LBP at baseline, for women and men separately. Continuous and categorical variables are shown in separate tables. Each table contains one column showing characteristics of all individuals included in the statistical analysis, a second column showing the corresponding values of the cases reporting LBP at end of follow-up, and finally a third column for those lost during follow-up. The comparison referred to by the reviewer can be made by contrasting the first and third columns. We have also included some remarks about this comparison in the second paragraph of the discussion (and mentioned that similar results were found for respondents with LBP at baseline). Reviewer's remark: 4. Distribution of adjusting variables should be described in the sample (table). Our response: The relevant distributions of the variables adjusted for are now described by the first and second columns (for all individuals included in the analysis and those with LBP at end of follow-up, respectively) in supplementary tables 1-4. This applies to the cohort of indivduals without LBP at baseline, but the distributions were rather similar among those with LBP at baseline. The comparison between the two columns is also mentioned in the text itself in the first paragraph of the results section.