ARI values were significantly larger than would be expected under random

# Ari values were significantly larger than would be

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the cluster assignments (out of three labels) for each bootstrapped sample. ARI values were significantly larger than would be expected under random cluster assignment (Figure 3b). The mean and standard deviation of the bootstrapped ARI's for the cluster analysis were 0.537 and 0.203, respectively. The corresponding values for random group assignment were 0 and 0.033, respectively. Cohen's d for the difference in means using a pooled standard deviation was 3.69, suggesting significant stability in cluster agreement. The results of both bootstrapping simulations indicate that the partition of the data into three clusters is robust to changes in the data and hence suggests a replicable cluster structure in the population. Cluster characteristics— As expected, the clusters differed significantly with regard to the eye-tracking variables of %Scene, F (2,62) = 52.79, p = .0001; %Eyes, F (2,62) = 41.18, p < .001; and %Eye-to-Mouth, F (2,62) = 47.17, p < .001 (Figure 4, Table 2). Significant differences were also found for %Face, F (2,62) = 12.67, p < .001; %Mouth F (2,62) = 20.89, p < .001; and %Toys F (2,62) = 8.00, p < .001. Post-hoc comparisons (Figure 4, Table 2) indicated that toddlers in Cluster 1 exhibited a limited ability to attend to the scene in general compared to those in Clusters 2 ( p = .001) and 3 ( p = .001). When they attended to the scene, they spent less time looking at the speaker's face than toddlers in Clusters 2 ( p < .001) and 3 ( p = .002), and more time looking at the toys compared with Clusters 2 ( p = .008) and 3 ( p < .001). The time that toddlers in Cluster 1 spent looking at eyes was significantly lower than those in Cluster 2 ( p = .001) and marginally higher than those in Cluster 3 ( p = .064). Proportion of time looking at the mouth in Cluster 1 was comparable to that observed in Cluster 2 ( p = .205), but lower than in Cluster 3 ( p = .001). Although their overall attention to the faces was very limited, their eye- to-mouth ratio ( M =38%, SD =17) was greater than in Cluster 3 ( M =15%, SD =8; p < .001) and smaller than in Cluster 2 ( M =52%, SD =13; p = .003). Toddlers in Clusters 2 and 3 showed comparable ( p = .784) attention to the scene and did not differ significantly in their looking ratios to the Face ( p = .398) or Toys ( p = .505). They did, however, differ in how they distributed attention to the key facial features of eyes ( p = . 001) and mouth ( p = .001). When looking at the speaker's face, toddlers in Cluster 3 almost exclusively focused on her mouth, leading to a significantly lower Eye to Mouth ratio compared to Clusters 1 ( p = .001) and 2 ( p < .003). In comparison, those in Cluster 2 divided their attention to eyes and mouth almost equally. Campbell et al. Page 6 J Autism Dev Disord . Author manuscript; available in PMC 2015 February 01. NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript
Clinical Characteristics of the Identified Clusters Intensity of intervention— A comparison of the average number of hours per week of intervention in the three clusters indicated no significant differences, F (2,47) = .17, p = .848.

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• Fall '08
• Staff
• The Land, Daniel J. Campbell

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