K. Gorman et al., "Children's Use of Disfluencies Distinguish ASD and Language Impairment", IMFAR 2014 (emphasis added):
This study compares the relative frequencies of "uh" and "um" in the spontaneous speech of children with ASD (with or without comorbid language impairment) to two control groups. Methods: Participants: 112 children ages 3;10–9;0 participated: ASD (50), Specific Language Impairment (SLI; 18), and Typical Development (TD; 44). All diagnoses were verified by best-estimate clinical consensus. The children with ASD were split into two groups: one group with comorbid language impairment (ALI) as diagnosed by a CELF Core Language Score below 85, and one group with ASD but no clinical language impairment (ALN). All children were high functioning monolingual English speakers. Data collection: a clinician administered the Autism Diagnostic Observation Schedule (ADOS; module 2 or 3) to each child. Sessions were recorded and transcribed.
Results: For all group pairs, diagnosis was uncorrelated with overall (i.e., "uh" + "um") rate of filled pause use. FP choice was analyzed for each comparison set using mixed effects logistic regression, with chronological age, FSIQ, ADOS "activity", and utterance position (utterance-initial vs. non-initial) as covariates. Diagnosis was a significant predictor for ALN/TD (p = .001) and ALI/SLI (p = .038); in both comparisons the ASD group used fewer instances of "um". Diagnosis was non-significant for TD/SLI (p = .888) and ALI/ALN (p = .814). ALI and ALN groups both used "uh" and "um" at an approximately 1:1 ratio, whereas TD and SLI groups used "um" 2 to 3 times more often than "uh". ADOS "activity" and utterance position were also significant predictors of FP choice; remaining covariates were non-significant.