[1] Med Univ S Carolina, Dept Med & Biometry, Charleston, SC 29425 USA
[2] Med Univ S Carolina, Dept Bioinformat & Epidemiol, Charleston, SC 29425 USA
[3] McGill Univ, Dept Med, Montreal, PQ H3A 2T5, Canada
[4] McGill Univ, Dept Epidemiol & Biostat, Montreal, PQ H3A 2T5, Canada
[5] Univ British Columbia, Dept Med, Vancouver, BC V5Z 1M9, Canada
[6] McMaster Univ, Hamilton, ON L8S 4L8, Canada
[7] Univ Western Ontario, London, ON N6A 3K7, Canada