As is indicated in , MTFC girls had higher mean levels of homework completion and school attendance than GC girls at both postbaseline assessments. To test our first hypothesis (examining main effects of group condition on school engagement outcomes), three ANCOVAs (3- to 6-month homework completion, 12-month homework completion, and 12-month school attendance) were conducted. In the homework ANCOVAs, the baseline homework score was entered as a covariate; in the school attendance ANCOVA, the baseline school attendance score was entered as a covariate. In all three ANCOVAs, intervention group condition was entered as the predictor (1 [MTFC]; 0 [GC]).
The ANCOVA for homework completion while in the treatment setting indicated a significant effect for group, F(1, 70) = 6.01, p < .05, with MTFC girls having spent significantly more days on homework during treatment than GC girls. The ANCOVA for homework completion at 12 months postbaseline indicated both a significant effect of baseline homework completion, F(1, 68) = 4.93, p < .05, with higher baseline homework scores predicting higher homework scores at 12 months postbaseline, and a significant effect for group, F(1, 68) = 6.94, p < .01, with MTFC girls having higher homework scores than GC girls at 12 months postbaseline. The ANCOVA for school attendance indicated a significant effect for group, F(1, 68) = 5.28, p < .05, with the MTFC girls having significantly greater attendance than GC girls at 12 months postbaseline. The overall model tests and effect sizes are shown in .
| Table 2ANCOVA Models for Educational Engagement Outcomes |
To test our second hypothesis (examining whether homework completion during the intervention setting mediated the previously found effects of MTFC on days in locked settings [
Leve et al., 2005]), a path analysis was conducted using
AMOS 5.0 (
Arbuckle & Wothke, 2003). Full information maximum likelihood was used to estimate means, variances, and covariances for the missing cases based on the observed data. The examination of the estimated means and covariances using Little’s Missing Completely at Random test indicated that the data met the stringent assumption of missing completely at random, χ
2(4) = 1.72,
p = .787, suggesting the appropriateness of the full information maximum likelihood analyses.
Baron and Kenny’s (1986) guidelines were used for testing whether four mediating conditions were met: (a) a direct effect of intervention group on the 12-month outcome in the absence of the mediating variable, (b) a direct effect of intervention group on the mediating variable, (c) a direct effect of the mediating variable on the 12-month outcome, and (d) a decrease in significance of the direct path from intervention group to the 12-month outcome in the presence of the mediator (
Baron & Kenny, 1986;
Judd & Kenny, 1981).
The results of the path analysis are presented in . All four conditions for the mediational test were met: (a) the direct path from intervention group to 12-month number of days in locked settings was significant in the absence of the mediator (β = −.22, p < .05, not shown in ), (b) the direct effect of intervention group on homework completion while in the intervention setting was significant (β = .28, p < .05), (c) the direct effect from homework completion while in the intervention setting on 12-month days in locked settings was significant (β = −.28, p < .01), and (d) the path from intervention group to 12-month days in locked settings became nonsignificant in the presence of the mediator (β = −.13, ns). The overall model fit was acceptable, χ2 = .513, p = .47; CFI = 1.00; RMSEA = .00, and the predictors accounted for 8% of the variance in homework completion while in the intervention setting and 24% of the variance in 12-month days in locked settings.