[1] Caro Res, Concord, MA 01742 USA
[2] McGill Univ, Fac Med, Montreal, PQ, Canada
[3] McGill Univ, Dept Epidemiol Biostat & Occupat Med, Montreal, PQ, Canada
[4] St Louis Univ, Dept Hlth Policy & Management, St Louis, MO 63103 USA
[5] Good Hope Hosp, Dept Cardiol, Sutton Coldfield, W Midlands, England