Table 2.

Means (SD) for Substance Abuse Treatment Variables and p-Values contrasting the two CM Schedules

	Total Sample (N=90)	Escalating Reinforcement Condition (n=52)	Fixed Reinforcement Condition (n=38)	t	df	p-value
Number of drug-negative urine samples	7.8 (4.4)	8.1 (4.5)	7.4 (4.3)	0.75	81.9	0.46
Time point of first drug- positive urine sample	4.1 (4.9)	4.1 (5.1)	4.2 (4.2)	-0.10	86.7	0.92
Longest number of consecutive drug-negative urine samples	6.0 (4.5)	6.6 (4.6)	5.2 (4.2)	1.50	83.7	0.14
Number of opioid-negative urine samples	8.1 (4.2)	8.3 (4.3)	7.7(4.2)	0.66	80.9	0.51
Time point of first opioid- positive urine sample	4.3 (4.9)	4.3 (5.2)	4.2 (4.5)	0.10	85.4	0.92
Longest number of consecutive opioid- negative urine samples	6.2 (4.5)	6.9 (4.6)	5.3 (4.2)	1.71	83.7	0.09
Number of cocaine- negative urine samples	8.4 (4.3)	8.9 (4.3)	7.8(4.3)	1.20	79.9	0.23
Time point of first cocaine- positive urine sample	5.4 (4.9)	6.0 (5.2)	4.6 (4.4)	1.38	86.0	0.17
Longest number of consecutive cocaine- negative urine samples	6.3 (4.5)	7.0 (4.7)	5.4 (4.1)	1.72	85.2	0.09

Notes: Drug-negative was defined as a urine sample negative for opioids (excluding methadone) and cocaine; opioid-negative was defined as a urine sample negative for opioids excluding methadone. Values are M (SD). P-Values refer to comparisons between the escalating and fixed reinforcement conditions and are derived from an independent sample t-test assuming unequal variances and Welch's approximation for calculation of degrees of freedom.