Skip to main content

Table 3 Likelihood ratio (LR) test statistics for differential item functioning on the SF-36 physical functioning and mental health sub-scale items

From: Latent variable mixture models to test for differential item functioning: a population-based analysis

Item LR Statistic Δdf* p-value
Physical Functioning
 PF1: Vigorous activities 99.63 4 <0.0001
 PF2: Moderate activities 127.49 4 <0.0001
 PF3: Lifting or carrying groceries 151.04 4 <0.0001
 PF4: Climbing several flights of stairs 37.69 4 <0.0001
 PF5: Climbing one flight of stairs 60.95 4 <0.0001
 PF6: Bending, kneeling or stooping 141.85 4 <0.0001
 PF7: Walking more than a mile 87.79 4 <0.0001
 PF8: Walking several blocks 34.51 4 <0.0001
 PF9: Walking one block 3.26 2 0.196
 PF10: Bathing or dressing self 64.76 2 <0.0001
Mental Health
 MH1: Been a very nervous person? 71.79 3 <0.0001
 MH2: Felt so down in the dumps that nothing could cheer you up? 21.03 3 0.0001
 MH3: Felt calm and peaceful? 234.43 3 <0.0001
 MH4: Felt downhearted and blue? 52.27 3 <0.0001
 MH5: Been a happy person? 198.28 3 <0.0001
  1. LR statistics are for the comparison of nested models: (a) mixture IRT model with free thresholds across classes for each item, and (b) IRT model with constrained thresholds across classes for each item. The mixture IRT model accounted for local dependence. Note that the latent variable mixture model for the physical functioning sub-scale had 3 classes and the model for the mental health sub-scale had 2 classes. Δdf is the difference in degrees of freedom for models defined in (a) and (b)