Author Contributions: Dr Cardwell 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: Cardwell, Abnet, Cantwell, Murray.
Acquisition of data: Cardwell, Murray.
Analysis and interpretation of data: Cardwell, Abnet, Murray.
Drafting of the manuscript: Cardwell, Abnet, Murray.
Critical revision of the manuscript for important intellectual content: Cardwell, Abnet, Cantwell, Murray.
Statistical analysis: Cardwell, Abnet.
Obtained funding: Murray.
Administrative, technical, or material support: Cardwell, Cantwell.
Study supervision: Murray.
Financial Disclosures: None reported.
Funding/Support: Access to the GPRD database was funded through the Medical Research Council's license agreement with the UK Medicines and Healthcare Products Regulatory Agency. However, the interpretation and conclusions contained in this study are those of the authors alone.
Role of the Sponsor: The sponsor had no role in the design and conduct of the study; the collection, management, analysis, or interpretation of the data; or the preparation, review, or approval of the manuscript.
Additional Contributions: We thank Maciej Domanski, MSc (Centre for Public Health, Queen's University Belfast, Belfast, United Kingdom), for data management and Carmel Hughes, PhD (Clinical and Practice Research Group, School of Pharmacy, Queen's University Belfast), for commenting on the manuscript. Neither of these individuals received additional compensation for their contributions.