The means and standard deviations for the RBS-R, SQ, and BRIEF are included in . The ASD group scored significantly higher than typical comparisons on all subscales and the total/composite scores of these measures. An independent samples t-test was used to examine group differences between the ASD and TYP groups for repetitive behavior, sensory features, and executive functioning. In all analyses, the t-test assumed unequal variances resulting in a significant difference (p < .0001).
Means and Standard Deviations for RBS-R, SQ, and BRIEF
Group Differences in Repetitive Behaviors
The mean group difference (i.e., difference in the mean value between the two groups) is reported for the 5 factor-derived RBS-R subscale scores and the total score. The mean values per group can be found in . For Stereotypy, the mean group difference was -5.09 with 95% confidence interval [-6.12, -4.06]. For Self-injury, the mean group difference was -2.37 with 95% confidence interval [-3.03, -1.70]. For Compulsions, the mean group difference was -2.76 with 95% confidence interval [-3.52, -2.01]. For Sameness behaviors, the mean group difference was -7.06 with 95% confidence interval [-8.48, -5.64]. For Restricted Interests, the mean group difference was -2.83 with 95% confidence interval [-3.38, -2.29]. For the RBS-R total score, the mean group difference was -20.11 with 95% confidence interval [-23.41, -16.80].
Group Differences in Sensory Issues
Based on the SQ composite score, the mean group difference was -5.18 with 95% confidence interval [-5.92, -4.45].
Group Differences in Executive Functioning
For the BRIEF Behavior Regulation Index, the mean group difference was -24.22 with 95% confidence interval [-27.37, -21.08]. For the Metacognition Index, the mean group difference was -22.75 with 95% confidence interval [-25.74, -19.77]. For the BRIEF composite score, the mean group difference was -25.46 with 95% confidence interval [-28.39, -22.53].
Relationship between RBS-R, SQ, and BRIEF
Pearson correlation coefficients were used to examine relationships between the three measures within the ASD group. The SQ composite score was moderately correlated with the Stereotypy (r = 0.41, p = .004) and Compulsions (r = 0.34, p = .020) subscales of the RBS-R and the total score (r = 0.35, p = .017). Only the Behavioral Regulation Index of the BRIEF was moderately correlated with the RBS-R subscales of Self-injury (r = 0.38, p = .003), Compulsions (r = 0.39, p = .002), Rituals/Sameness (r = 0.40, p = 0.002) and the RBS-R total score (r = 0.43, p = .001). No significant correlations were found between the BRIEF and the SQ composite score. See for correlations between the three measures.
Correlations between measures, ASD group (n = 61)
A regression analysis was used to predict the RBS-R total score. The outcome variable was log-transformed prior to analysis to produce residuals that were approximately normal. Because the natural log of zero is undefined, and many individuals in the TYP group had scores of zero on the RBS-R, an offset of 0.50 was added to the scores prior to transformation. The residuals obtained after transformation were approximately normal but exhibited slight heteroskedastisticity. Robust standard errors were utilized to correct for any resulting underestimation of the standard errors that could lead to an inflated risk of Type I error. All predictor variables were centered to their values in the typical group. The variables that best predicted the clinical expression of repetitive behaviors using the RBS-R total score were group (TYP vs. ASD; b = 1. 706, p < 0.001), chronological age in months (b = -0.004, p = 0.031), SQ composite score (b = 0.097, p = 0.026), and the BRIEF Behavioral Regulation Index (b = 0.033, p = 0.003). A diagnosis of ASD, lower chronological age, and higher scores on the SQ and the BRIEF Behavioral Regulation Index were predictive of more repetitive behaviors. The combination of these variables resulted in r2 = 0.86, thus these variables accounted for 86% of the variance in the total RBS-R score. Mothers' (p = 0.092) or fathers' education levels (p = 0.469), Leiter-R IQ scores (p = 0.577), and BRIEF Metacognition scores (p = 0.200) were not predictive of RBS-R scores.