Author Contributions: Dr Kulkarni had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Study concept and design: Kulkarni, Aziz, Shams, Busse.
Acquisition of data: Kulkarni, Aziz, Shams, Busse.
Analysis and interpretation of data: Kulkarni, Busse.
Drafting of the manuscript: Kulkarni.
Critical revision of the manuscript for important intellectual content: Kulkarni, Aziz, Shams, Busse.
Statistical analysis: Kulkarni, Busse.
Administrative, technical, or material support: Aziz, Shams.
Financial Disclosures: None reported.
Funding/Support: Dr Busse is funded by a New Investigator Award from the Canadian Institutes of Health Research and the Canadian Chiropractic Research Foundation.
Role of the Sponsor: The Canadian Institutes of Health Research and the Canadian Chiropractic Research Foundation had no role in the design and conduct of the study; the collection, analysis, and interpretation of the study; or in the preparation, review, or approval of the manuscript.
Additional Contributions: We thank Stephen D. Walter, PhD (Department of Biostatistics and Clinical Epidemiology, McMaster University, Hamilton, Ontario, Canada), for his advice in the drafting of the manuscript. Dr Walter did not receive compensation for his statistical advice.