In an attempt to compare the success of anticoagulation control in all arenas, Walraven and associates examined 67 studies involving 50 208 patients with 57 154 patient-years from anticoagulation clinics, clinical trials, and community practises. Study investigators examined many variables which may have influenced differences in therapeutic control and concluded that study setting was the greatest predictor. They quoted the following rates of anticoagulation success: PSM 72%, RCT's 66%, anticoagulation clinics 66%, and community primary care clinics 57%. It was also shown that PSM was associated with a significant improvement in anticoagulation control.