. Author manuscript; available in PMC: 2013 Dec 25.

Published in final edited form as: Psychol Addict Behav. 2012 Dec 31;27(4):10.1037/a0031065. doi: 10.1037/a0031065

Table 2.

Percent days abstinent at each follow-up time point by PR/NR status and between-group effect sizes estimates (Cohen’s d)

	PR group (M, SD)	NR group (M, SD)	Test	Sig	Cohen’s d	Interpretation of effect size
0-month	43.9 (33.1)	47.9 (35.9)	t(107)= −.588	.558	0.116	Negligible
3-month	47.7 (33.4)	61.8 (34.9)	t(100)= −2.08	.040	0.413	Medium
6-month	40.8 (34.2)	57.0 (38.4)	t(97)= −2.21	.029	0.446	Medium
12-month	43.5 (36.9)	47.8 (32.6)	t(92)= −.602	.549	0.124	Negligible

PR=Positive Reinforcement group; NR=negative reinforcement group; M= mean; SD= standard deviation. Sig= statistical significance level.