Comparison 2. Trials on mastectomy.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
2.1 Incidence of postoperative seroma	10	629	Risk Ratio (M‐H, Fixed, 95% CI)	1.02 [0.90, 1.15]
2.2 Mean volume of seroma	6	411	Std. Mean Difference (IV, Random, 95% CI)	‐0.24 [‐0.63, 0.15]
2.3 Total volume of drained seroma	10	629	Std. Mean Difference (IV, Random, 95% CI)	‐0.83 [‐1.50, ‐0.17]
2.4 Number of days for persistent drainage	9	539	Std. Mean Difference (IV, Random, 95% CI)	‐0.36 [‐0.71, ‐0.01]
2.5 Surgical site infection	8	522	Risk Ratio (M‐H, Fixed, 95% CI)	1.13 [0.60, 2.10]
2.6 Postoperative complications	5	437	Risk Ratio (M‐H, Fixed, 95% CI)	1.35 [0.59, 3.12]
2.7 Length of hospital stay	4	169	Std. Mean Difference (IV, Fixed, 95% CI)	0.28 [‐0.02, 0.59]