A multinational observational cohort study in acutely ill medical patients of practices in prevention of venous thromboembolism: findings of the International Medical Prevention Registry on Venous Thromboembolism (IMPROVE) - Tapson,V.F.; Decousus,H.; Piovella,F.; Zotz,R.B.; Allegrone,J.; Anderson,F.A. (Blood, 2003)