Supplementary Materials
Table S1: Item Response Theory Analysis: Item discrimination and difficulty parameters: Rounds 1 & 2
(a) Round 1 (b) Round 2
Ite m No.
Item discrimination Item difficulty
Item discrimination
Item difficulty
1 2 3 1 2 3
1 2.81 (0.28) -1.67 (0.14) -0.69 (0.09) -0.03 (0.08) 2.79 (0.29) -1.67 (0.14) -0.69 (0.09) -0.03 (0.08) 2 1.27 (0.15) -1.31 (0.17) 0.00 (0.11) 0.79 (0.14)
3 3.41 (0.37) -1.32 (0.11) -0.90 (0.09) -0.34 (0.08) 3.41 (0.39) -1.32 (0.11) -0.91 (0.09) -0.35 (0.08) 4 1.56 (0.17) -1.82 (0.19) -0.78 (0.12) 0.07 (0.10)
5 2.34 (0.24) -1.18 (0.12) -0.56 (0.09) -0.01 (0.08) 2.25 (0.24) -1.2 (0.12) -0.57 (0.09) -0.01 (0.08) 6 1.63 (0.18) -1.46 (0.16) -0.62 (0.11) 0.13 (0.10)
7 2.56 (0.28) -2.23 (0.19) -1.28 (0.12) -0.53 (0.09) 2.56 (0.29) -2.22 (0.19) -1.28 (0.12) -0.53 (0.09) 8 0.94 (0.13) -0.77 (0.17) 0.52 (0.15) 1.23 (0.20)
9 0.89 (0.13) -2.45 (0.36) -1.18 (0.21) -0.08 (0.14) 10 0.81 (0.13) -0.60 (0.18) 0.86 (0.19) 1.59 (0.27)
11 2.47 (0.24) -1.13 (0.11) -0.41 (0.09) 0.32 (0.08) 2.52 (0.25) -1.13 (0.11) -0.42 (0.08) 0.32 (0.08) 12 1.87 (0.20) -1.39 (0.15) -0.66 (0.10) -0.03 (0.09) 1.93 (0.21) -1.38 (0.14) -0.65 (0.10) -0.03 (0.09) 13 2.27 (0.25) -2.20 (0.20) -1.25 (0.12) -0.66 (0.09) 2.29 (0.26) -2.19 (0.2) -1.25 (0.12) -0.66 (0.09) 15 2.19 (0.24) -1.92 (0.17) -0.97 (0.11) -0.47 (0.09) 2.24 (0.25) -1.91 (0.17) -0.97 (0.11) -0.47 (0.09) 16 1.50 (0.16) -1.09 (0.14) -0.36 (0.11) 0.39 (0.11)
17 1.93 (0.20) -1.18 (0.13) -0.47 (0.10) 0.24 (0.09) 1.81 (0.19) -1.22 (0.13) -0.49 (0.10) 0.24 (0.09) 18 1.22 (0.14) -1.31 (0.17) -0.36 (0.12) 0.58 (0.13)
19 0.88 (0.12) -3.23 (0.46) -0.89 (0.18) 0.64 (0.17)
21 2.20 (0.22) -0.76 (0.10) 0.09 (0.08) 0.58 (0.09) 2.25 (0.24) -0.76 (0.10) 0.09 (0.08) 0.58 (0.09) 22 1.98 (0.21) -2.04 (0.19) -0.99 (0.12) -0.34 (0.09) 2.01 (0.22) -2.03 (0.19) -0.98 (0.11) -0.34 (0.09) 23 1.73 (0.20) -2.53 (0.26) -1.62 (0.17) -0.46 (0.10)
24 1.08 (0.14) -0.09 (0.13) 1.20 (0.18) 2.18 (0.29)
25 1.98 (0.21) -1.53 (0.15) -0.72 (0.10) -0.17 (0.09) 2.02 (0.22) -1.52 (0.15) -0.72 (0.10) -0.17 (0.09)
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Note: The discrimination (slope) parameter describes how well the item discriminates between respondents with low or high scores on the item set. In a GRM model, it is not equivalent to the peak of the item information function. Item difficulty values indicate the theta score (the estimated level of latent trait EDA for each
participant) where there is a
≥
50% chance of being rated 1 (i.e., “Some-what true”), 2 (i.e., “Mostly true”), or 3 (i.e., “Very true”). Standard errors for estimates are presented in parentheses.2
Table S2: Differential Item Functioning analysis: Likelihood-Ratio Test Results
Item No. Age Gender Ability level Independence in
daily living chi2(4) p-value chi2(4) p-value chi2(4) p-value chi2(4) p-value
1 Obsessively resists demands 6.77 0.149 6.02 0.198 4.18 0.382 1.98 0.740
3 Driven by the need to be in charge 1.42 0.841 3.12 0.538 2.77 0.597 0.60 0.963
5 Bossy, doesn't apply rules to self 3.64 0.457 3.14 0.534 6.71 0.152 6.53 0.163
7 Demands must be carefully presented 6.19 0.186 1.45 0.836 6.08 0.193 7.65 0.105
11 Good at getting round others 4.39 0.356 0.05 1.000 13.12 0.011* 8.62 0.071
12 Unaware of difference between self/authority 2.09 0.719 7.02 0.135 6.23 0.182 8.29 0.082
13 If pressurized may have a meltdown 2.52 0.641 3.05 0.550 16.66 0.001* 6.42 0.170
15 Mood changes rapidly 1.59 0.811 4.21 0.378 5.00 0.287 3.37 0.498
17 Blames or targets specific person 11.31 0.023* 4.09 0.394 2.25 0.690 7.70 0.103
21 Outrageous behavior to avoid 3.33 0.504 2.95 0.567 5.29 0.259 2.74 0.602
22 Extreme response to small events 5.98 0.201 1.26 0.868 1.40 0.845 8.36 0.079
25 Negotiates better terms with adults 6.09 0.192 4.48 0.345 15.92 0.003* 8.68 0.070
Note: Items in italic showed evidence of differential item functioning (DIF) and were thus removed from the final item bank. * p <.05.
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Table S3: Item Response Theory Analysis: Final round (after DIF analysis)
Item
No. Item
discrimination
Item difficulty
1 2 3
1 3.09 (0.35) -1.62 (0.13) -0.68 (0.09) -0.04 (0.08) 3 3.31 (0.4) -1.33 (0.11) -0.92 (0.09) -0.36 (0.08) 5 2.07 (0.23) -1.25 (0.13) -0.6 (0.1) -0.02 (0.09) 7 2.75 (0.32) -2.17 (0.19) -1.26 (0.12) -0.52 (0.08) 12 1.86 (0.21) -1.4 (0.15) -0.67 (0.1) -0.04 (0.09) 15 2.29 (0.26) -1.88 (0.17) -0.97 (0.11) -0.48 (0.09) 21 2.23 (0.25) -0.76 (0.1) 0.08 (0.08) 0.57 (0.09) 22 2.07 (0.24) -2.01 (0.19) -0.97 (0.11) -0.34 (0.09)
Note: The discrimination (slope) parameter describes how well the item discriminates between respondents with low or high scores on the item set. In a GRM model, it is not equivalent to the peak of the item
information function. Item difficulty values indicate the theta score (the estimated level of latent trait EDA for each participant) where there is a
≥
50% chance of being rated 1 (i.e., “Some-what true”), 2 (i.e., “Mostly true”), or 3 (i.e., “Very true”). Standard errors for estimates are presented in parentheses.4
Table S4: Z-scores for differences between correlation coefficients for EDA-8 and conceptually distinct subscales vs. EDA-8 and Reactivity, EDA-8 and Demand Specific non-compliance, and EDA-8 and Socially Inflexible non-compliance.
EDA-8 - Reactivity EDA-8 – Demand
Specific EDA-8 – Socially Inflexible Z-score p-value Z-score p-value Z-score p-value Child behavior
EDA-8 - Hyperactivity -6.95 <.001* -4.28 <.001* -5.51 <.001*
EDA-8 - Peer problems -7.11 <.001* -4.44 <.001* -5.67 <.001*
EDA-8 - Conduct problems -0.82 .415 1.86 .063 0.62 .536
EDA-8 - Emotional problems -6.67 <.001* -4.00 <.001* -5.23 <.001*
EDA-8 - Prosocial behavior -10.12 <.001* -7.45 <.001* -8.68 <.001*
EDA-8 - Dysphoria -3.07 .002* -0.39 .694 -1.63 .103
Child ASD severity
EDA-8 - Social interaction -8.24 <.001* -5.56 <.001* -6.79 <.001*
EDA-8 - Social Communication -8.71 <.001* -6.03 <.001* -7.26 <.001*
EDA-8 - RRBIs -7.02 <.001* -4.35 <.001* -5.58 <.001*
EDA-8 - SCQ Total score, -7.60 <.001* -4.93 <.001* -6.16 <.001*
Note: Comparison of Spearman’s rho correlation coefficients using Fisher’s r to z transformation for bivariate correlations. Sample size for all bivariate correlations = 233. Correction for multiple comparisons (30
comparisons, alpha = .002). * Indicates survived correction for multiple comparisons.
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Table S5: Z-scores for differences between correlation coefficients for EDA-8 and conceptually distinct subscales vs. Reactivity and conceptually distinct subscales, Demand Specific non-compliance and conceptually distinct subscales, and Socially Inflexible non-compliance and conceptually distinct subscales.
EDA-8 – subscale vs. Reactivity -
subscale
EDA-8 – subscale vs. Demand Specific - subscale
EDA-8 – subscale vs. Socially Inflexible - subscale
Z-score p-value Z-score p-value Z-score p-value Child behavior
Hyperactivity -0.78 .436 0.01 .989 -0.28 .777
Peer problems 0.65 .513 0.29 .775 0.06 .950
Conduct problems 1.18 .239 3.48 .001* 3.11 .002*
Emotional problems -0.71 .477 -0.01 .993 0.06 .954
Prosocial behavior 0.48 .630 0.41 .680 1.22 .222
Dysphoria -3.18 .001* 0.34 .735 0.40 .686
Child ASD severity
Social interaction -0.87 .385 -0.75 .451 -0.54 .590
Social Communication -1.22 .222 -1.03 .302 -1.68 .093
RRBIs 0.07 .947 -1.01 .313 -0.42 .672
SCQ Total score, -1.07 .284 -1.02 .306 -1.09 .274
Note: Comparison of Spearman’s rho correlation coefficients using Fisher’s r to z transformation for bivariate correlations. Sample size for all bivariate correlations = 233 to ensure comparability of estimates. Correction for multiple comparisons (30 comparisons, alpha = .002). * Indicates survived correction for multiple comparisons.
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Supplementary Figure
Figure S1: Frequency distributions for EDA-8 and other relevant measures (a) EDA-8
(b) EDI Reactivity
(c) HSQ Demand Specific non-compliance
(d) HSQ Socially Inflexible non-compliance
Note: Sample sizes for (b) – (d) are 232-233 because these measures were only available for Sample 2.
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Figure S2: Relations between EDA-8 and Social Communication Questionnaire total score
Note: rs = .07, p > .1
