00373nas a2200145   4500000000100000000000100001008004100002100001300043700001500056700001400071245011100085300001000196490000700206022001400213       2012                            d1 aR. Platt1 aJ. Delaney1 aS. Suissa00aThe positivity assumption and marginal structural models: the example of warfarin use and risk of bleeding  a77-830 v27  a0393-2990