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Table 3 Differential item functioning results comparing autistic and general population adults on 9-item unidimensional model

From: Improving the measurement of alexithymia in autistic adults: a psychometric investigation of the 20-item Toronto Alexithymia Scale and generation of a general alexithymia factor score using item response theory

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
  1. Results indicate omnibus Wald tests of differential item functioning using the iterative anchor-selection method of Cao et al. (2017). P values (pFDR) 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 (pFDR < 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)
  2. 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
  3. bPractically significant DIF (i.e., wABC > 0.3)