[1] Univ Calif San Francisco, Dept Epidemiol & Biostat, San Francisco, CA 94143 USA
[2] Costello Med Consulting Inc, Boston, MA USA
[3] Costello Med Consulting Ltd, London, England
[4] Gilead Sci Europe Ltd, Uxbridge, England
[5] Gilead Sci Inc, Foster City, CA USA
[6] Univ Calif San Diego, Dept Med, Div Pulm Crit Care & Sleep Med, San Diego, CA USA
[7] Imperial Coll London, Sch Publ Hlth, London, England
[8] Imperial Coll London, Natl Heart & Lung Inst, London, England