Comparison 1. All surgeries.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1.1 Transfusions	82	12520	Risk Ratio (M‐H, Random, 95% CI)	0.65 [0.59, 0.72]
1.1.1 CV (vascular)	4	266	Risk Ratio (M‐H, Random, 95% CI)	0.61 [0.32, 1.15]
1.1.2 CV (no bypass)	3	169	Risk Ratio (M‐H, Random, 95% CI)	0.82 [0.69, 0.97]
1.1.3 CV (with bypass)	25	2676	Risk Ratio (M‐H, Random, 95% CI)	0.81 [0.73, 0.89]
1.1.4 Obstetrics	1	1349	Risk Ratio (M‐H, Random, 95% CI)	0.82 [0.39, 1.74]
1.1.5 Orthopaedic (hip)	14	1641	Risk Ratio (M‐H, Random, 95% CI)	0.52 [0.37, 0.72]
1.1.6 Orthopaedic (knee)	21	2214	Risk Ratio (M‐H, Random, 95% CI)	0.47 [0.35, 0.65]
1.1.7 Orthopaedic (spinal)	3	194	Risk Ratio (M‐H, Random, 95% CI)	0.44 [0.31, 0.63]
1.1.8 Orthopaedic (mixed)	11	4011	Risk Ratio (M‐H, Random, 95% CI)	0.64 [0.45, 0.90]
1.2 Transfusions (sensitivity: registration)	58	6353	Risk Ratio (M‐H, Random, 95% CI)	0.62 [0.55, 0.70]
1.2.1 CV (vascular)	4	266	Risk Ratio (M‐H, Random, 95% CI)	0.61 [0.32, 1.15]
1.2.2 CV (no bypass)	3	169	Risk Ratio (M‐H, Random, 95% CI)	0.82 [0.69, 0.97]
1.2.3 CV (with bypass)	20	1756	Risk Ratio (M‐H, Random, 95% CI)	0.79 [0.70, 0.89]
1.2.4 Obstetrics	1	1349	Risk Ratio (M‐H, Random, 95% CI)	0.82 [0.39, 1.74]
1.2.5 Orthopaedic (hip)	7	585	Risk Ratio (M‐H, Random, 95% CI)	0.47 [0.27, 0.80]
1.2.6 Orthopaedic (knee)	13	1210	Risk Ratio (M‐H, Random, 95% CI)	0.40 [0.26, 0.60]
1.2.7 Orthopaedic (spinal)	2	145	Risk Ratio (M‐H, Random, 95% CI)	0.54 [0.34, 0.85]
1.2.8 Orthopaedic (mixed)	8	873	Risk Ratio (M‐H, Random, 95% CI)	0.53 [0.39, 0.72]
1.3 Transfusions (sensitivity: low risk of bias (ROB))	17	6398	Risk Ratio (M‐H, Random, 95% CI)	0.74 [0.61, 0.89]
1.3.1 CV (vascular)	1	100	Risk Ratio (M‐H, Random, 95% CI)	0.92 [0.70, 1.19]
1.3.2 CV (no bypass)	1	61	Risk Ratio (M‐H, Random, 95% CI)	0.59 [0.19, 1.81]
1.3.3 CV (with bypass)	5	1344	Risk Ratio (M‐H, Random, 95% CI)	0.82 [0.70, 0.97]
1.3.4 Obstetrics	1	1349	Risk Ratio (M‐H, Random, 95% CI)	0.82 [0.39, 1.74]
1.3.5 Orthopaedic (hip)	1	200	Risk Ratio (M‐H, Random, 95% CI)	0.36 [0.26, 0.51]
1.3.6 Orthopaedic (knee)	4	544	Risk Ratio (M‐H, Random, 95% CI)	0.66 [0.29, 1.50]
1.3.7 Orthopaedic (spinal)	1	50	Risk Ratio (M‐H, Random, 95% CI)	0.50 [0.05, 5.17]
1.3.8 Orthopaedic (mixed)	3	2750	Risk Ratio (M‐H, Random, 95% CI)	0.74 [0.35, 1.59]
1.4 Transfusions (subgroup: timing)	82	12520	Risk Ratio (M‐H, Random, 95% CI)	0.66 [0.59, 0.72]
1.4.1 Intraoperative	20	3193	Risk Ratio (M‐H, Random, 95% CI)	0.70 [0.60, 0.82]
1.4.2 Postoperative	52	5710	Risk Ratio (M‐H, Random, 95% CI)	0.58 [0.50, 0.68]
1.4.3 Intra‐ and postoperative	13	3617	Risk Ratio (M‐H, Random, 95% CI)	0.84 [0.71, 1.00]
1.5 Transfusions (subgroup: transfusion threshold)	82	12520	Risk Ratio (M‐H, Random, 95% CI)	0.65 [0.59, 0.72]
1.5.1 Restrictive (Hb ≦ 80 g/L)	27	5967	Risk Ratio (M‐H, Random, 95% CI)	0.72 [0.61, 0.85]
1.5.2 Liberal (Hb > 80 g/L)	35	3461	Risk Ratio (M‐H, Random, 95% CI)	0.59 [0.50, 0.69]
1.5.3 No threshold/protocol reported	20	3092	Risk Ratio (M‐H, Random, 95% CI)	0.64 [0.49, 0.83]