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Table 4 Tests for differential item functioning on the SF-12 mental health (MH) and physical health (PH) sub-scale items, stratified by type of joint replacement

From: Differential item functioning of the SF-12 in a population-based regional joint replacement registry

Item THA TKA
Δχ2 df p-value Δχ2 df p-value
MH Sub-scale
 M1 20.09 6 0.003 37.03 6 < 0.001
 M2 31.85 6 < 0.001 73.22 6 < 0.001
 M3 38.30 6 < 0.001 44.61 6 < 0.001
 M4 99.26 6 < 0.001 83.93 6 < 0.001
 M5 * * * * * *
 M6 * * * * * *
PH Sub-scale
 P1 244.32 6 < 0.001 425.16 6 < 0.001
 P2 * * * * * *
 P3 27.97 6 < 0.001 53.76 6 < 0.001
 P4 12.96 6 0.044 16.34 6 0.012
 P5 19.78 6 0.003 20.25 6 0.003
 P6 * * * * * *
  1. df Degree of freedom, Δχ2 = Chi-square difference test obtained using the DIFFTEST procedure for WLSMV in MPlus; * = anchor item; All tests are statistically significant at α = 0.05