A review of data sharing statements in observational studies published in the BMJ: A cross-sectional study

This exploratory analysis contributes to the literature on biomedical data sharing practices, and demonstrates the importance of the further understanding of data sharing policies, practices, and barriers for domain and type specific data sets, such as those associated with observational studies.

While it does not impact the soundness of this short report, I would recommend that the authors expand on their reasoning for choosing BMJ for their analysis.  Specifically, while BMJ requires data sharing statements, its data sharing policy is relatively general (sharing is encouraged, but specific requirements are not communicated).  It would be helpful for the authors to discuss (potentially as a follow-up analyses), how the robustness of a journal's data sharing policy could influence the rate of data sharing.

Regarding the sampling methodology, the authors write, "All observational research articles published in the BMJ between 1st January 2015 and 31st August 2017 were investigated. These dates were chosen as it provides a reasonable sample size for analysis and recent data post-dating some of the articles regarding clinical trial data sharing."  In my view, this statement is insufficient.  The authors should provide more detailed and quantitative information about the strength and the nature of the sample.

Finally, the authors write "A review of the data sharing statements of these studies revealed that 149 (63%) studies had a statement implying that the data underlying the study could not be share".  However the methodology does not indicate if the data "could" be shared, only if it was shared.  I would urge the authors to revise this statement be be more precise.