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Table 2 Differential item functioning by modes of administration for anxiety

From: Score equivalence of paper-, tablet-, and interactive voice response system-based versions of PROMIS, PRO-CTCAE, and numerical rating scales among cancer patients

Anxiety McFadden pseudo R2 change (\({R}_{2}^{2}-{R}_{1}^{2}\)) McFadden pseudo R2 change (\({R}_{3}^{2}-{R}_{2}^{2}\)) McFadden pseudo R2 change (\({R}_{3}^{2}-{R}_{1}^{2}\))
I felt fearful 0.0001 0.0007 0.0005
I found it hard to focus on anything other than my anxiety 0.0041 0.0051 0.0010
My worries overwhelmed me 0.0019 0.0028 0.0008
I felt uneasy 0.0007 0.0015 0.0008
I felt nervous 0.0017 0.0023 0.0006
I felt like I needed help for my anxiety 0.0015 0.0029 0.0014
I felt anxious 0.0002 0.0004 0.0001
I felt tense 0.0011 0.0015 0.0003
(NRS) describe the level of anxiety on average 0.0005 0.0005 0.0000
(PRO-CTCAE) How often did you feel anxiety? 0.0049 0.0058 0.0009
(PRO-CTCAE) What was the severity of your anxiety at the WORST? 0.0025 0.0025 0.0000
(PRO-CTCAE) How much did anxiety interfere with usual/daily activities? 0.0009 0.0017 0.0008
  1. A base model (model 1) posits that only the trait level predicts responses. A second model (model 2) has both trait level and group as independent variables. If model 2 predicts item responses statistically significantly better than model 1 (i.e., McFadden pseudo R2 change (\({R}_{2}^{2}-{R}_{1}^{2}\)) ≥ 0.02), then there is uniform DIF. In uniform DIF, DIF has a consistent impact across trait levels. If the model that includes an interaction term between trait and group (model 3) fits significantly better than model 2 (i.e., McFadden pseudo R2 change (\({R}_{3}^{2}-{R}_{2}^{2}\)) ≥ 0.02), then the impact of DIF varies by trait level (nonuniform DIF). If model 3 fits significantly better than model 1 (i.e., McFadden pseudo R2 change (\({R}_{3}^{2}-{R}_{1}^{2}\)) ≥ 0.02), there is overall or total DIF