. Author manuscript; available in PMC: 2017 Jul 1.

Published in final edited form as: Addiction. 2016 Apr 1;111(7):1226–1234. doi: 10.1111/add.13327

Table 2. Comparison of propensity scores between samples in 10 National Institute of Drug Use Clinical Trial Network (CTN) randomized controlled trials (RCTs) and target samples from the Treatment Episodes Data-Admission (TEDS-A).

Study type	Study Number	Mean propensity score		∆p^a	Pooled standard deviation	Standardized ∆p^b	t-test	p-value
Study type	Study Number	RCT	TEDS-A	∆p^a	Pooled standard deviation	Standardized ∆p^b	t-test	p-value
Buprenorphine/Naloxone (Bup/Nx) Detoxification	CTN0001	0.69	0.19	0.50	0.25	2.07	22.94	<0.001
	CTN0002	0.64	0.25	0.39	0.23	1.67	24.99	<0.001
	CTN0003	0.70	0.25	0.45	0.26	1.72	38.99	<0.001
	CTN0010	0.69	0.21	0.48	0.24	2.03	25.32	<0.001
	CTN0030	0.80	0.20	0.60	0.28	2.08	53.12	<0.001
Motivational enhancement/interviewing	CTN0004	0.61	0.30	0.31	0.23	1.35	28.65	<0.001
	CTN0005	0.57	0.33	0.24	0.23	1.06	21.74	<0.001
	CTN0013	0.65	0.27	0.38	0.23	1.63	21.19	<0.001
Motivational incentives	CTN0006	0.57	0.32	0.25	0.21	1.20	25.23	<0.001
Motivational incentives	CTN0007	0.62	0.28	0.34	0.23	1.46	27.59	<0.001
Pooled results
	Pooled standardized		95% CI		Heterogeneity statistics
	Pooled standardized		95% CI		I²^c	χ² (df)	p-value
Overall	1.54		1.49 – 1.60		94.6%	165.45 (df = 9)	<0.001
Buprenorphine/Naloxone(Bup/Nx) Detoxification	1.90		1.81 – 1.98		79.6%	19.57 (df = 4)	<0.001
Motivational enhancement/interviewing	1.28		1.18 – 1.37		89.2%	18.51 (df = 2)	<0.001
Motivational incentives	1.31		1.21 – 1.42		83.3%	5.97 (df = 1)	0.02

∆p is difference between propensity scores of CTN RCT sample and TEDS-A samples.

Standardized ∆p is computed as ∆p divided by pooled standard deviation.

I² is the percentage of observed total variation across studies that is due to heterogeneity rather than chance. It is calculated as I² = 100% × (Q - df)/Q, where Q is Cochran's heterogeneity statistic and df the degrees of freedom (see text for further information).