RT Journal Article SR Electronic T1 Bias when using dead controls to study handgun purchase as a risk factor for violent death JF Injury Prevention JO Inj Prev FD BMJ Publishing Group Ltd SP 381 OP 382 DO 10.1136/ip.9.4.381 VO 9 IS 4 A1 D J Wiebe A1 C C Branas YR 2003 UL http://injuryprevention.bmj.com/content/9/4/381.abstract AB