Table 3.

Differential item functioning results comparing autistic and general population adults on 9-item unidimensional model

TAS-20 Item #	χ2(5)	pFDR	wABC	ESSD	Parametersa
1	35.30	< 0.001	0.089	− 0.018	a1, d1, d2
2	23.18	< 0.001	0.164	0.157	d2, d3
3	65.10	< 0.001	0.433b	0.670b	d2, d3, d4
9	26.03	< 0.001	0.064	− 0.021	d1
11	30.47	< 0.001	0.165	0.001	a1, d2, d3
12	30.19	< 0.001	0.149	− 0.187	d1
13	57.66	< 0.001	0.064	− 0.022	a1, d1, d2, d3, d4
14	61.90	< 0.001	0.031	− 0.022	a1, d1, d2, d3, d4

Results indicate omnibus Wald tests of differential item functioning using the iterative anchor-selection method of Cao et al. (2017). P values (p_FDR) are corrected for a 5% false discovery rate using the Benjamini–Hochberg procedure. Parameters that were significantly different between groups when tested alone with follow-up Wald tests (p_FDR < 0.05) are indicated in the Parameters column. TAS-20 = 20-item Toronto Alexithymia Scale; wABC = weighted area between curves; ESSD = expected score standardized difference (in Cohen’s d metric); a₁ = slope parameter; d₁–d₄ = item intercept parameters (i.e., item “difficulty” parameters)

^aParameters in bold are larger (i.e., more discriminating for a parameters and “easier” for d parameters) in the autistic group. Larger values of a indicate that the item is more strongly related to the latent trait in autistic adults, whereas larger values of d indicate that a given item response is endorsed at lower latent trait levels in autistic adults relative to the general population

^bPractically significant DIF (i.e., wABC > 0.3)