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

Table 4 GAFS-8 graded response model parameters and equivalent factor loadings for full sample

TAS-20 Item #	a₁	d₁	d₂	d₃	d₄	λ	h²
1	2.802	3.092	− 0.689	− 2.740	− 6.336	0.855	0.731
2	2.190	3.478	0.491	− 0.931	− 3.841	0.790	0.623
6	2.335	2.090	− 0.805	− 2.413	− 5.497	0.808	0.653
9	2.402	3.137	0.072	− 1.434	− 5.170	0.816	0.666
11	1.870	2.745	− 0.234	− 1.505	− 4.340	0.740	0.547
12	1.235	1.739	− 0.526	− 1.636	− 3.644	0.587	0.345
13	1.892	2.054	− 0.646	− 2.231	− 4.771	0.743	0.553
14	1.538	1.285	− 1.133	− 2.201	− 4.361	0.671	0.450

Parameters estimated using maximum marginal likelihood based on Bock–Aitkin EM algorithm. This model contained two groups: general population (θ fixed to M = 0, SD = 1 in this group) and autistic group (mean and SD of θ free to vary), with all item parameters constrained to equality between groups. TAS-20 = 20-item Toronto Alexithymia Scale; a₁ = slope parameter; d₁–d₄ = item intercept parameters (more positive values indicate “easier” items); λ = factor loading on single factor; h² = communality (squared factor loading)

ISSN: 2040-2392