The number of patients overall, and in intervention and control group for randomised controlled trials: stockings, was 3392 overall,532 in the intervention group, and 2860 in the control group; Intermittent pneumatic compression was 927 overall, 395 in the intervention group, and 532 in the control group; Heparin and dihydroergotamine was 1089 overall, 557 in the intervention group, and 532 in the control group; Heparin was 3514 overall, 2982 in the intervention group, and 532 in the control group; Heparin and stockings, was 674 overall, 142 in the intervention group, and532 in the control group; Intermittent pneumatic compression and stockings, was 289 overall, 137 in the intervention group, and 532 in the control group.