Table 5. Fixed effects for the three-level piecewise-linear growth model fitted to the IRT scale scores including main effects and interactions with study membership.

Fixed Effects Estimates
Effect	Estimate	Standard Error	DF	t Value	Pr > |t|
Intercept	.234	.037	1222	6.35	<.0001
Piece #1	−.038	.009	6161	−4.08	<.0001
Piece #2	.007	.017	6161	0.43	.667
Piece #3	−.043	.005	6161	−8.08	<.0001
MLS	−.240	.065	1222	−3.71	.0002
AHBP	−.388	.048	1222	−8.01	<.0001
MLS*Piece #1	.021	.013	6161	1.65	.1
AHBP*Piece #2	−.183	.021	6161	−8.56	<.0001
AHBP*Piece #3	.034	.007	6161	4.78	<.0001

note: Piece #1 spans ages 10 to 18; Piece #2 spans ages 18 to 21; Piece #3 spans ages 21 to 33. Intercept defined at age 21. MLS=Michigan Longitudinal Study; AHBP=Adolescent Health and Behavior Project; symbol “*” reflects interaction. Model estimated with random effects at all three levels, but these are not presented here.