Dealing with missing standard deviation and mean values in meta-analysis of continuous outcomes: a systematic review

Table 2 GALA results: missing SD

			Method for missing SD replacement
	Complete data result		Ma [23]		Walter [18]		Cochrane Handbook [4]		None, omit study
	Mean difference (days)	95% confidence interval	Bias	Imprecision	Bias	Imprecision	Bias	Imprecision	Bias	Imprecision
Scenario
5 trials	− 0.01	(− 0.87, 0.85)
2 missing SD			0.21	1.18	0.05	1.05	−0.01	0.73	0.27	1.28
10 trials	−0.01	(− 0.37, 0.35)
2 missing SD			0.04	1.04	−0.01	1.01	−0.02	1.97	0.02	1.06
5 missing SD			−0.03	1.56	0.01	1.10	−0.12	2.40	0.00	1.64
20 trials	0.00	(−0.31, 0.30)
5 missing SD			0.07	1.26	0.02	1.02	0.06	2.74	0.02	1.25
10 missing SD			0.26	2.20	0.02	1.07	0.17	3.93	0.05	1.41
30 trials	−0.01	(−0.28, 0.25)
5 missing SD			0.06	1.11	0.03	1.06	−0.12	2.23	0.09	1.15
10 missing SD			−0.09	1.49	−0.01	1.13	−0.21	2.45	−0.02	1.62
15 missing SD			−0.03	1.87	0.02	1.17	−0.23	2.28	0.12	2.19

Results are given for mixed sample size scenario (average of 60 patients per trial) and random allocation of trials to missing SD values. Imprecision is the ratio of the widths of the confidence intervals for the intervention effect [width when estimating missing SDs: width when all SDs available]. Results for other scenarios (small trials, large trials; missing SD in small trials, large trials) show similar patterns and are available in online Additional file 3 Tables S1-S8

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