Extended anticoagulation compared to placebo after three months of therapy for a first episode of idiopathic venous thromboembolism - Kearon, C; Gent, M; Hirsh, J; Weitz, J; Kovacs, MJ; Anderson, D; Turpie, AG; Green, D; Ginsberg, JS; Wells, P; MacKinnon, B; Julian, JA; Johnston, M; Douketis, J; van Nguyen, P; Kassis, J; Dolan, S; Demers, C; Desjardins, L; Solymoss, S; Trowbridge, A; Roberts, R (N Engl J Med, 1999)