Empirical Challenges in Defining Treatments and Time in the Evaluation of Gun Laws.

From the *Department of Epidemiology, Biostatistics & Occupational Health, McGill University †Department of Ethics, Equity and Policy, McGill University. Editor’s Note: Related articles appear on pages. The authors report no conflicts of interest. Correspondence to: Sam Harper, Department of Epidemiology, Biostatistics & Occupational Health, McGill University, 2001 Avenue McGill College, Suite 1200, Montreal, QC H3A 1G1. E-mail: [email protected].