Table 4. Fixed and random effects for the three-level piecewise-linear growth model fitted to the IRT scale scores.
| Random Effects Estimates | ||||
|---|---|---|---|---|
| Effect | Estimate | Standard Error | Z Value | Pr Z |
| Intercept | 0.258 | 0.030 | 8.57 | <.0001 |
| Piece #1 | 0.010 | 0.002 | 5.89 | <.0001 |
| Piece #2 | 0.025 | 0.005 | 4.80 | <.0001 |
| Piece #3 | 0.002 | 0.001 | 3.12 | 0.0009 |
| Family | 0.081 | 0.015 | 5.48 | <.0001 |
| Residual | 0.294 | 0.007 | 40.53 | <.0001 |
| Fixed Effects Estimates | |||||
|---|---|---|---|---|---|
| Effect | Estimate | Standard Error | DF | t Value | Pr > |t| |
| Intercept | −0.034 | 0.024 | 1224 | −1.40 | 0.1618 |
| Piece #1 | 0.001 | 0.006 | 6164 | 0.18 | 0.8605 |
| Piece #2 | −0.092 | 0.010 | 6164 | −9.30 | <.0001 |
| Piece #3 | −0.019 | 0.004 | 6164 | −5.39 | <.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. Only variance components are presented, although the full matrix of variance and covariance terms were estimated in the growth model.