Table 5.

Evidence for predictive validity: Prediction of abstinence from marijuana use and related problems and symptoms at 6 months from initial readiness

Variable	IRR		ISA		ISR		ISTS
	Estimate	SE	Estimate	SE	Estimate	SE	Estimate	SE
6-month PDA
Fixed effects
Sex (1 = female, 2 = male)	−8.24	6.87	−6.86	6.84	−7.24	6.92	−7.65	6.83
Age	−3.06	2.66	−3.31	2.71	−2.96	2.68	−3.75	2.67
Race (1 = White, 2 = other)	−7.57	9.41	−7.93	9.48	−8.59	9.59	−7.44	9.38
ADT: #inpt. + #residential days, last 30 days	1.64	0.81*	1.62	0.82*	1.73	0.83*	1.56	0.81*
BL PDA, last 30 days	0.39	0.08*	0.40	0.08**	0.41	0.08**	0.36	0.08**
Initial readiness	1.52	1.25	3.37	5.38	−1.02	2.85	6.54	3.24*
Random effects
Intercept (site differences)	20.90	44.66	23.45	46.45	26.23	48.16	21.51	44.32
Residual	1,622.61	184.67**	1,637.98	187.02**	1,644.22	188.29**	1,606.91	187.02**
n	159		158		157		157
6-month RMPI
Fixed effects
Sex	−1.04	0.36**	0.86	0.36*	0.92	0.38*	0.83	0.36*
Age	−0.01	0.14	0.05	0.14	−0.02	0.14	0.04	0.14
Race	−0.08	0.55	−0.12	0.55	−0.04	0.56	−0.18	0.54
ADT	0.08	0.05	0.08	0.05	0.06	0.05	0.08	0.05
BL RMPI	0.04	0.01**	0.04	0.01**	0.03	0.01**	0.04	0.01**
Initial readiness	−0.17	0.06**	−0.79	0.28**	0.10	0.20	−0.57	0.17**
Random effects
Intercept	0.11	0.17	0.14	0.18	0.17	0.20	0.07	0.14
Residual	4.16	0.50**	4.13	0.50**	4.35	0.53**	4.09	0.49**
n	143		142		142		142
6-month DSMS
Fixed effects
Sex	0.53	0.30	0.43	0.30	0.45	0.30	0.36	0.29
Age	0.10	0.11	0.11	0.12	0.09	0.12	0.14	0.11
Race	0.91	0.42*	0.95	0.43*	0.93	0.43*	0.89	0.42*
ADT	0.08	0.03*	0.08	0.03*	0.08	0.03*	0.08	0.08*
BL DSMS	0.48	0.07**	0.46	0.07**	0.49	0.08**	0.49	0.07**
Initial readiness	−0.15	0.05**	−0.24	0.22	−0.09	0.14	−0.46	0.13**
Random effects
Intercept	0.05	0.10	0.09	0.13	0.11	0.13	0.04	0.09
Residual	2.73	0.32**	2.82	0.33**	2.86	0.34**	2.69	0.32**
n	149		148		148		148

Notes: A square root transformation was applied to the Rutgers Marijuana Problem Index (RMPI) and alcohol and other drug treatment (ADT) data. ns differ because of missing data, and parameter estimates are unstandardized. IRR = Initial Readiness Ruler; ISA = Initial Staging Algorithm; ISR = Initial SOCRATES Recognition; ISTS = Initial SOCRATES Taking Steps; PDA = percentage of days abstinent, measured by use of the Timeline Followback Interview and references 30 days before the interview date; inpt. = inpatient; BL = baseline; DSMS = Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, marijuana abuse and dependence symptom count.

^*p≤.05;

^**p≤.01.