Conception and design: Clarke, Gokaslan, Wolinsky. Acquisition of data: Clarke, Zadnik, Groves. Analysis and interpretation of data: Clarke, Zadnik, Groves. Drafting the article: Clarke, Zadnik, Groves, Sciubba, Wolinsky. Critically revising the article: all authors. Reviewed submitted version of manuscript: all authors. Approved the final version of the manuscript on behalf of all authors: Clarke. Statistical analysis: Clarke, Wolinsky. Administrative/technical/material support: Clarke. Study supervision: Clarke.