Table 3.

Subgroup analyses of associations between effect sizes and study characteristics (Hedges's g).^a

		Ncomp	g	95% CI	I 2	95% CI	P b
All studies		18	0.30	0.19 to 0.41***	50	13–71
2 possible outliers removedc		16	0.31	0.23 to 0.39***	0	0–52
Primary substance	Anyd	9	0.32	0.15 to 0.49***	69	38–85	0.146
	Opioids	5	0.36	0.20 to 0.53***	0	0–85
	Stimulants	4	0.13	–0.05 to 0.31	0	0–85
Subgroup analyses (n = 18)
Control groupe	Active	13	0.31	0.16 to 0.46***	62	31–79	0.978
	Non‐active	5	0.31	0.17 to 0.45***	0	0–79
Type	CRA + CM	6	0.39	0.26 to 0.52***	0	0–75	0.382
	MI	5	0.30	0.16 to 0.44***	0	0–79
	CBT	4	0.19	0.02 to 0.35	17	0–87
	Other	3	0.34	–0.18 to 0.85	90	74–96
Format	Add‐on	10	0.41	0.30 to 0.52***	12	0–54	0.011
	Standalone	8	0.17	0.03 to 32*	43	0–75
Type of assessment	Tox. screening	12	0.42	0.32 to 0.52***	0	0–58	0.016
	Self‐report	11	0.26	0.05 to 0.42*	71	46–84
Screening	DSM‐IV	9	0.42	0.27 to 0.56***	22	0–63	0.048
	Cut‐off scores	9	0.21	0.07 to 0.36**	55	4–79
Medication	Yes	6	0.34	0.19 to 0.48***	0	0–75	0.774
	No	3	0.22	–0.06 to 0.50	67	0–91
	NR	9	0.30	0.11 to 0.50**	67	34–84
Analyses	ITT analyses	13	0.31	0.20 to 0.42***	36	0–67	0.883
	Comp. analyses	5	0.33	0.04 to 0.63*	69	20–88
Recruitment	Clinical	10	0.34	0.18 to 0.49***	63	28–82	0.341
	Community	8	0.23	0.01–0.37**	11	0–71
Setting	Computer, out‐patient clinic	9	0.36	0.26 to .47***	0	0–65	0.002
	Computer, hospital	4	0.23	–0.44 to 0.50	71	19–90
	Internet, home	3	0.11	–0.07 to 0.29	0	0–90
	Computer, university	1	0.12	–0.33 to 0.56	0	NA
	Computer, residential centre	1	0.82	0–50 to 1.14***	0	NA
Female‐only studies	Yes	3	0.37	0.20 to 0.55***	0	0–90	0.448
	No	15	0.29	0.16 to 0.42***	57	23–76

BI = brief intervention; CET = cognitive enhancement therapy; Comp. = completers; EDUC = psychoeducation; ITT = intention‐to‐treat; MI = motivational interviewing; NA = not applicable; Ncomp = number of comparisons; NR = not reported; PA = positive affect; TAU = treatment as usual; Tox. = toxicology; WLC = waiting‐list control.

^aAccording to the random‐effects model;

^bthe P‐values in this column indicate if the difference between the effect sizes in the subgroups is significant; CI = confidence interval (*P ≤ 0.05; **P < 0.01; ***P ≤ 0.001);

^c 57, 58.

^dBy the term ‘any illicit substances’ we describe individuals who use at least one illicit substance and are included in transdiagnostic interventions targeting various substances at once.

^eActive controls include: TAU, MI, BI, EDUC; inactive controls include: WLC, add‐on.