Comparison 1. Music therapy vs. 'placebo' therapy or standard care.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Social interaction	3		SMD (Fixed, 95% CI)	Subtotals only
1.1 Non‐generalised	1		SMD (Fixed, 95% CI)	1.06 [0.02, 2.10]
1.2 Generalised (outside sessions, daily life)	3		SMD (Fixed, 95% CI)	0.71 [0.18, 1.25]
2 Communicative skills: non‐verbal	5		SMD (Fixed, 95% CI)	Subtotals only
2.1 Non‐generalised	3		SMD (Fixed, 95% CI)	0.57 [0.29, 0.85]
2.2 Generalised (outside sessions, daily life)	3		SMD (Fixed, 95% CI)	0.48 [‐0.02, 0.98]
3 Communicative skills: verbal	6		SMD (Fixed, 95% CI)	0.33 [0.16, 0.49]
3.1 Non‐generalised	4		SMD (Fixed, 95% CI)	0.33 [0.16, 0.50]
3.2 Generalised (outside sessions, daily life)	2		SMD (Fixed, 95% CI)	0.30 [‐0.28, 0.89]
4 Initiating behaviour	3		SMD (Fixed, 95% CI)	Subtotals only
4.1 Non‐generalised	3		SMD (Fixed, 95% CI)	0.73 [0.36, 1.11]
5 Social‐emotional reciprocity	1		SMD (Fixed, 95% CI)	Subtotals only
5.1 Non‐generalised	1		SMD (Fixed, 95% CI)	2.28 [0.73, 3.83]
6 Social adaptation	4		SMD (Fixed, 95% CI)	0.41 [0.21, 0.60]
6.1 Non‐generalised	3		SMD (Fixed, 95% CI)	1.15 [0.69, 1.61]
6.2 Generalised (outside sessions, daily life)	1		SMD (Fixed, 95% CI)	0.24 [0.02, 0.46]
7 Joy	1		SMD (Fixed, 95% CI)	0.96 [0.04, 1.88]
8 Quality of parent‐child relationship	2		SMD (Fixed, 95% CI)	0.82 [0.13, 1.52]