**3. Results**

*3.1. Prevalence of ASD* ASD Classification

In the current sample, 37.3% of participants met the overall classification criteria for ASD on the ADOS-2 (i.e., DS + ASD). The prevalence of ASD was higher among those receiving Module 2 (46.7%) than among those receiving Module 3 (26.3%); statistical comparisons indicated that this difference in rate between modules approached significance (*F*(1,82) = 3.722; *p* = 0.057; η <sup>2</sup> = 0.044). See Figure 1 for distribution of participant scores.

**Figure 1.** Frequency distribution of ADOS-2 CSSs across sample; (**a**) ADOS-2 Overall CSS for overall sample; (**b**) ADOS-2 RRB-CSS for overall sample; (**c**) ADOS-2 SA-CSS for overall sample. Note: Dotted line represents CSS cutoff for ASD classification. **Figure 1.** Frequency distribution of ADOS-2 CSSs across sample; (**a**) ADOS-2 Overall CSS for overall sample; (**b**) ADOS-2 RRB-CSS for overall sample; (**c**) ADOS-2 SA-CSS for overall sample. Note: Dotted line represents CSS cutoff for ASD classification.

Analyses were also conducted to determine whether participants classified as DS + ASD differed from participants classified as DS-only on CSS scores for the SA and RRB subdomains. In the overall sample, group differences were detected in both the SA (*F*(1,82) = 151.740; *p* < 0.001; η <sup>2</sup> = 0.652) and RRB domains (*F*(1,82) = 20.115; *p* < 0.001; η <sup>2</sup> = 0.199), such that individuals with DS + ASD had higher scores than those with DSonly. When exploring group differences at the module level, significant differences were detected for both SA-CSS (*F*(1,44) = 76.495; *p* < 0.001; η <sup>2</sup> = 0.640) and RRB-CSS for Module 2 (*F*(1,44) = 35.350; *p* < 0.001; η <sup>2</sup> = 0.451); however, only SA-CSS significantly differentiated groups in Module 3 (*F*(1,37) = 64.184; *p* < 0.001; η <sup>2</sup> = 0.641). Please see Figure 2 for means.

exploring group differences at the module level, significant differences were detected for both SA-CSS (*F*(1,44) = 76.495; *p* < 0.001; η<sup>2</sup> = 0.640) and RRB-CSS for Module 2 (*F*(1,44) = 35.350; *p* < 0.001; η<sup>2</sup> = 0.451); however, only SA-CSS significantly differentiated groups in

Module 3 (*F*(1,37) = 64.184; *p* < 0.001; η<sup>2</sup> = 0.641). Please see Figure 2 for means.

**Figure 2.** Group differences in mean ADOS-2 CSSs; (**a**) Group differences in mean ADOS-2 CSSs for overall sample; (**b**) Group differences in mean ADOS-2 CSSs for Module 2; (**c**) Group differences in mean ADOS-2 CSSs for Module 3. **Figure 2.** Group differences in mean ADOS-2 CSSs; (**a**) Group differences in mean ADOS-2 CSSs for overall sample; (**b**) Group differences in mean ADOS-2 CSSs for Module 2; (**c**) Group differences in mean ADOS-2 CSSs for Module 3.

## *3.2. Group Differences across Characteristics 3.2. Group Differences across Characteristics*

We compared the participants classified as DS + ASD to participants classified as DSonly in terms of chronological age, nonverbal cognitive ability, lexical diversity, and syntactic complexity (see Table 2). Significant group differences were found for nonverbal cognitive ability (*F*(1,82) = 1.091; *p* = 0.044; η<sup>2</sup> = 0.053), lexical diversity (*F*(1,82) = 7.330 *p* = 0.008; η<sup>2</sup> = 0.085), and syntactic complexity (*F*(1,82) = 4.198; *p* = 0.000; η<sup>2</sup> = 0.168), such that group means were lower for participants classified as DS + ASD than for participants classified as DS-only across all comparisons. The differences in lexical diversity and syntactic complexity, but not nonverbal cognitive ability, remained significant after We compared the participants classified as DS + ASD to participants classified as DS-only in terms of chronological age, nonverbal cognitive ability, lexical diversity, and syntactic complexity (see Table 2). Significant group differences were found for nonverbal cognitive ability (*F*(1,82) = 1.091; *p* = 0.044; η <sup>2</sup> = 0.053), lexical diversity (*F*(1,82) = 7.330 *p* = 0.008; η <sup>2</sup> = 0.085), and syntactic complexity (*F*(1,82) = 4.198; *p* = 0.000; η <sup>2</sup> = 0.168), such that group means were lower for participants classified as DS + ASD than for participants classified as DS-only across all comparisons. The differences in lexical diversity and syntactic complexity, but not nonverbal cognitive ability, remained significant after applying the FDR correction.

applying the FDR correction. Follow up analyses were conducted to determine whether differences found in lexical diversity and syntactic complexity were also seen for each of the modules analyzed separately. Results of these analyses revealed that, within Module 2, participants classified as DS + ASD produced C-units with less syntactic complexity (*F*(1,42) = 7.095 *p* = 0.011; η<sup>2</sup> = 0.148) than participants classified as DS-only. Similar results were found for Module 3, with a lower mean for syntactic complexity (*F*(1,37) = 5.201 *p* = 0.029; η<sup>2</sup> = 0.126) found for participants classified as DS + ASD than DS-only. No significant differences in lexical diversity was found between individuals who were classified as DS + ASD and those classified as DS-only in either Module 2 (*F*(1,42) = 2.484 *p* = 0.123; η<sup>2</sup> = 0.057) or Module 3 (*F*(1,37) = 1.125 *p* = 0.296; η<sup>2</sup> = 0.030). Follow up analyses were conducted to determine whether differences found in lexical diversity and syntactic complexity were also seen for each of the modules analyzed separately. Results of these analyses revealed that, within Module 2, participants classified as DS + ASD produced C-units with less syntactic complexity (*F*(1,42) = 7.095 *p* = 0.011; η <sup>2</sup> = 0.148) than participants classified as DS-only. Similar results were found for Module 3, with a lower mean for syntactic complexity (*F*(1,37) = 5.201 *p* = 0.029; η <sup>2</sup> = 0.126) found for participants classified as DS + ASD than DS-only. No significant differences in lexical diversity was found between individuals who were classified as DS + ASD and those classified as DS-only in either Module 2 (*F*(1,42) = 2.484 *p* = 0.123; η <sup>2</sup> = 0.057) or Module 3 (*F*(1,37) = 1.125 *p* = 0.296; η <sup>2</sup> = 0.030).


**Table 2.** Means for Participants Characteristics for overall sample, Module 2 and Module 3.

Note: CA = Chronological age; SB-5 NV Change Sensitive Score = Stanford Binet-5 Non-Verbal Change Sensitive Score.
