Autism spectrum disorder (ASD) is a heterogeneous neurodevelopmental condition that affects an estimated 1 in 44 children in the US, with a male-to-female ratio of approximately 4:1. 1 The prevalence of diagnosed ASD has increased substantially over the past 2 decades, although this increase in prevalence has been greater in certain demographic groups, such as female patients 2 and those from minoritized racial ethnic groups, 3 suggesting the presence of diagnostic disparities by race and sex. 4 Notably, the prototypical behavioral manifestations of ASD (on which existing diagnostic criteria and standardized diagnostic instruments are based) were derived from samples of children who were predominantly White and male, 4 and, thus, systematic biases in the diagnostic tools used to evaluate individuals with suspected ASD could theoretically contribute to observed diagnostic disparities.Kalb et al 5 sought to investigate this issue by quantifying the magnitude and practical impact of race-based and sex-based bias in the Autism Diagnostic Observation Schedule, Second Edition (ADOS-2), a clinician-administered measure that is widely used in both research and clinical practice to establish or confirm a diagnosis of ASD. Leveraging ADOS-2 data from 6269 youth attending specialist diagnostic evaluations at a university-based ASD clinic, the authors 5 quantified the degree to which different versions (ie, modules) of the ADOS-2 systematically underestimated the features of ASD in Black/African American children (vs White children) and female children (vs male children).Although their analysis did reveal significant race-based bias in 8 items and sex-based bias in 5 items, 5 estimated effect size metrics 6 indicated that for all but 2 items (D4, Repetitive Interest [racebased bias], and D2, Hand Mannerisms [sex-based bias]), these effects were small and unlikely to be of practical significance. Moreover, for all ADOS-2 modules tested, the maximum difference in expected ADOS-2 total scores attributable to measurement bias was less than 1 scale point (range, 0.07-0.91 point). 5 Overall, these findings indicate that the degree of race and sex bias present in the ADOS-2 is low and unlikely to contribute to the systematic underdiagnosis of ASD in Black or female children.A major strength of the study by Kalb et al 5 is its innovative use of item response theory (IRT) models to examine the ADOS-2 items and quantify the degree of bias (or differential item functioning [DIF] in IRT terms) between demographic groups. IRT is a modern, large-sample, psychometric method used to develop, evaluate, and score psychological tests, 7 and IRT models provide mathematical descriptions of how certain item responses (eg, the endorsement of a symptom on the ADOS-2 as 0, 1, or 2) relate to unmeasured latent variables (ie, ASD severity in the case of the ADOS-2) that are assumed to underlie all items on the scale. Within an IRT framework, researchers are able to test for DIF between groups by examining whether a given item is differentially relate...