In order to determine whether the frequency and duration measures could be used for analyses or whether rate and proportion of RSB needed to be derived as a function of the length of the samples, the mean lengths of the samples across groups were compared. The mean lengths (and standard deviations) of the Behavior Samples in minutes for the three groups were as follows: ASD: 21.5 (5.3); DD: 21.4 (3.4); and TD: 21.9 (3.9). No differences in sample length were found between any groups (ASD-DD: p<.94; ASD-TD: p<.59; DD-TD: p< .61). As a final check, rate (frequency/sample length) and proportion (duration/sample length) measures were calculated for the composite RSB measures (see below) and subjected to ANOVA comparisons. There were no differences in the pattern of results obtained from the frequency and duration measures. Therefore, the raw frequency and duration data were used for all analyses.
RSB in the Second Year
A summary of the means, standard deviations, and effect sizes of group differences for each RSB coded in the study is provided in for frequency measures and for duration. All RSB included in the coding system were demonstrated by some children, except for covering ears in response to a sensory stimulus, which no children demonstrated. In addition, the ASD group did not demonstrate lining up or stacking objects, or sniffs/smells in the sensory category and no one in the TD group demonstrated rolling objects, or sniffs/smells. It is evident in and , that most group differences were in the expected direction (i.e., the ASD group had larger mean scores), with the exception of two behaviors. Specifically, both the DD and TD groups demonstrated lining up or stacking of objects, while the ASD group did not. In addition, only one child in the DD group demonstrated one instance of sniffing/smelling. In light of these results, a subset of behaviors that showed differences in the expected direction for both groups (i.e., effect sizes with a positive value) with small effect sizes (d=.20), or with a medium effect size (d=.50) with one group was selected and a composite RSB score was calculated for each category of RSB. For RSB with objects, this included the following behaviors: bang/taps, rocks/flips, swipes, spins/wobbles, rolls, moves/places, and clutches. RSB with body included bangs surface, rubs body, and stiffens, and the sensory composite included feels/touches, fixates, and sucks fingers.
Mean Frequencies of Individual Repetitive and Stereotyped Behaviors Across Groups
Mean Duration in Seconds of Individual Repetitive and Stereotyped Behaviors across Groups
A priori one-tailed contrasts were then calculated between the ASD and TD and ASD and DD groups to determine whether the ASD group demonstrated more RSB than the DD and TD groups on the composite measures of RSB with objects, RSB with body and sensory behaviors. Levene’s test of homogeneity of variance was significant for all categories of RSB; therefore contrasts were calculated without assuming equal variance. The results are presented in . Using the subset of behaviors included in the composites, children with ASD demonstrated significantly higher frequency and duration of RSB with objects, RSB with body, and sensory behaviors than both the TD and the DD groups. The effect sizes of the differences were moderate and large for the RSB with objects and RSB with body categories, and small for the sensory behaviors. The means and standard deviations for the sensory behaviors indicate many children had no or very low sensory behaviors causing the distribution of the data to be skewed. Where sensory behaviors were observed, the large SD in relation to the mean suggests variability among the children in all groups, which may have masked group differences. Group differences in sensory behaviors must therefore be viewed with caution, and sensory behaviors were not included in any further analyses. In addition, it should be noted that because the patterns for frequency and duration measures of RSB were very similar in this analysis, only the frequency data were used in the remaining analyses.
Frequency and Duration of Repetitive and Stereotyped Behaviors Across Groups
Concurrent Relationships with other Second Year Measures
Concurrent relations between RSB frequency measures and other second year measures were examined in the ASD group alone, as well as in the ASD and DD groups combined in order to explore the relationship between RSB and other second year measures in children with ASD specifically, as well as in the combined group of children with communication delays in the second year. Correlations are presented in . Significant correlations were observed between RSB with objects and developmental level on the symbolic composite that were moderate in the ASD group alone, and small in the ASD and DD groups combined. Significant moderate correlations were observed between RSB with objects and the social composite in both the ASD group and the ASD and DD groups combined, while small correlations were observed between RSB with body and the social composite that were only significant in the combined group. In light of the relationship between RSB and the symbolic composite, these correlations were recalculated controlling for developmental level. Only the relationship between RSB with objects and the social composite in the ASD and DD groups combined remained significant, with a small effect (pr=.26; p<.05).
Correlations between Repetitive and Stereotyped Behaviors in the Second Year and Second and Fourth Year Measures
Predictive Relationships with Fourth Year Outcome Measures
To examine predictive relations between early RSB and developmental outcomes, bivariate correlations controlling for age between the RSB measures in the second year and verbal and nonverbal scores on the MSEL and the adaptive behavior composite of the VABS were computed. To examine predictive relations between early RSB and autism symptoms at 3 years, bivariate correlations controlling for age were examined between frequency of RSB in the second year and severity of autism symptoms based on the ADOS algorithm scores for repetitive and restricted behaviors (RRB) and social affect (SA) at three years. Results are presented in .
In the children with ASD, significant moderate correlations were observed between RSB with objects in the second year and verbal and nonverbal DQ on the MSEL at three years. These were no longer significant when controlling for developmental level on the symbolic composite in the second year. There were no significant correlations between early RSB and outcome on the VABS, or autism symptoms on the ADOS in the ASD group. Similar patterns between early RSB with objects and outcome on the MSEL were noted in the combined ASD and DD groups. The relationship between RSB with objects and nonverbal DQ remained significant (pr=.25; p<.05) even when controlling for developmental level on the symbolic composite. In the combined ASD and DD groups, small to moderate significant correlations were observed between RSB with objects in the second year and RRB and SA symptoms in the fourth year, as well as a significant moderate correlation between RSB with body in the second year and RRB on the ADOS in the fourth year. When controlling for developmental level on the symbolic composite, correlations remained significant between RSB with objects and SA on the ADOS (pr=.35; p<.01) and between RSB with body and RRB on the ADOS (pr=.31; p<.01). The correlation between RSB with objects and RRB was no longer significant (pr=.19) and the correlation between RSB with body and SA symptoms remained largely unchanged (pr=.15). No significant correlations were observed between RSB with objects or body and the VABS adaptive behavior composite in the combined group of children with communication delays.