Author Contributions: Dr Basso 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: Basso, Rasmussen, Weinberg, Wilcox, Irgens, Skjaerven.
Acquisition of data: Irgens, Skjaerven.
Analysis and interpretation of data: Basso, Rasmussen, Weinberg, Wilcox, Irgens, Skjaerven.
Drafting of the manuscript: Basso, Rasmussen.
Critical revision of the manuscript for important intellectual content: Basso, Rasmussen, Weinberg, Wilcox, Irgens, Skjaerven.
Statistical analysis: Basso, Rasmussen, Weinberg, Irgens, Skjaerven.
Administrative, technical, or material support: Irgens, Skjaerven.
Financial Disclosures: None reported.
Funding/Support: This research was supported in part by the Intramural Research Program of the NIH, National Institute of Environmental Health Sciences.
Role of the Sponsor: No special funding was used for this study. Aside from the usual internal publication clearances, the authors' institutions had no role in the design and conduct of the study; the collection, management, analysis, and interpretation of the data; or the preparation, review, or approval of the manuscript.