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Table 2 Differential item functioning by gender and age for the 15 items of the FPDI pain and function subscales

From: A Rasch Analysis of the Manchester Foot Pain and Disability Index

Item Differential item functioning: gender Differential item functioning: age group
  Uniforma Non-uniformb Uniforma Non-uniformb
Functioning     
1. Avoid walking outside 0.2073 0.6787 0.7507 0.0786
2. Avoid walking long distances 0.2544 0.8759 0.7729 0.3730
3. Don't walk in a normal way 0.9714 0.0968 0.0895 0.9878
4. Walk slowly 0.0161 0.3659 0.6014 0.3262
5. Have to stop and rest feet 0.1247 0.5087 0.7701 0.3262
6. Avoid hard or rough surfaces 0.0673 0.4546 0.0014* 0.9992
7. Avoid standing for a long time 0.5544 0.8868 0.6841 0.1632
8. Catch the bus or use the car more often 0.4011 0.0614 0.9277 0.2543
9. Need help with housework or shopping 0.9402 0.9359 0.1205 0.8793
11. Get irritable when feet hurt 0.5657 0.2936 0.4229 0.9999
Pain     
10. Do everything with more pain or discomfort 0.1000 0.3845 0.6579 0.3527
14. Constant pain in feet 0.6385 0.0736 0.6426 0.5198
15. Feet are worse in the morning 0.4947 0.9999 0.1955 0.1860
16. Feet more painful in the evening 0.0878 0.7780 0.5688 0.8217
17. Get shooting pains in feet 0.4986 0.7282 0.6482 0.8619
  1. a Uniform DIF is assessed by the p-value associated with the main effect term in a 2-way ANOVA; b Non-uniform DIF is assessed by the p-value associated with the interaction term in a 2-way ANOVA; * Significant misfit after Bonferroni correction