TABLE 2—

Ordinary Least-Squares Regression Models Comparing Medicaid Enrollment Among Adults Entering Substance Use Disorder Treatment Programs in Massachusetts and in Comparison States Before and After 1997 MassHealth Eligibility Expansion: Treatment Episodes Data Set, 1992–2009

Independent Variables	b (SE)	P
Model 1a
Constant	16.55 (3.85)	<.001
Overall secular trend	−0.27 (1.35)	.84
Before-to-after 1997	−4.69 (5.06)	.36
Trend after 1997	1.07 (1.35)	.43
State	17.19 (5.45)	.004
State * overall secular trend	−2.47 (1.80)	.18
State * before-to-after 1997	25.90 (7.15)	.001
State * trend after 1997	4.33 (1.91)	.03
Model 2b
Constant	35.17 (5.20)	<.001
Overall secular trend	−3.05 (1.72)	.09
Before-to-after 1997	20.58 (6.82)	.01
Trend after 1997	5.59 (1.82)	.01
Homeless	−8.89 (7.35)	.24
Homeless * overall secular trend	1.81 (2.43)	.46
Homeless * before-to-after 1997	4.00 (9.65)	.68
Homeless * trend after 1997	−1.45 (2.57)	.58
Model 3c
Constant	33.74 (5.35)	<.001
Overall secular trend	−2.73 (1.77)	.14
Before-to-after 1997	21.21 (7.02)	.01
Trend after 1997	5.40 (1.87)	.01

^aComparison of change in Medicaid enrollment after 1997 among adults entering substance use disorder treatment programs in Massachusetts and comparison states (combined data from DC and AK, AZ, CO, HI, ID, IL, MD, MO, MT, ND, NE, NH, NJ, NV, PA, TX, and WV).

^bComparison of the impact of MassHealth on Medicaid enrollment among homeless and housed adults entering substance use disorder treatment programs in MA.

^cNonsignificant interactions removed.