Author Contributions: Ms Munk-Olsen and Mr Laursen had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.
Study concept and design: Munk-Olsen, Laursen, Pedersen, Mors, Mortensen.
Acquisition of data: Pedersen, Mortensen.
Analysis and interpretation of data: Munk-Olsen, Laursen, Pedersen, Mors.
Drafting of the manuscript: Munk-Olsen.
Critical revision of the manuscript for important intellectual content: Munk-Olsen, Laursen, Pedersen, Mors, Mortensen.
Statistical analysis: Munk-Olsen, Laursen.
Obtained funding: Mortensen.
Administrative, technical, or material support: Mortensen.
Study supervision: Pedersen, Mors, Mortensen.
Financial Disclosures: None reported.
Funding/Support: This study was supported by the Stanley Medical Research Institute, Chevy Chase, Md. Psychiatric epidemiological research at the National Centre for Register-Based Research is in part funded through a collaborative agreement with the Centre for Basic Psychiatric Research, Psychiatric Hospital, Aarhus, Denmark.
Role of the Sponsors: The sponsors of the study had no role in the design and conduct of the study, in the collection, analysis, and interpretation of the data, or in the preparation, review, or approval of the manuscript.
Previous Presentation: A part of this study was presented at the Marcé Society International Biennial Scientific Meeting, September 13, 2006, Keele University, Keele, England.