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Table 5 Differential item functioning (DIF) by age, gender and visual acuity

From: Catquest-9SF questionnaire: validation of Malay and Chinese-language versions using Rasch analysis

Version Item DIF by age DIF by gender DIF by VA
Item difficulty Diff in logits P-valuea Item difficulty Diff in logits P-valuea Item difficulty Diff in logits P-valuea
≤65 years >65 years Male Female VA >6/18 VA ≤6/18
Malay n= 141 94    107 129    76 108   
Daily-life activities in general −0.16 −0.20 0.04 0.866 −0.16 −0.16 0.00 >0.995 −0.49 0.01 −0.51 0.043
Satisfaction with vision −0.88 −0.66 −0.22 0.341 −0.77 −0.77 0.00 >0.995 −0.71 −0.87 0.16 0.515
Reading newspaper −0.77 −0.88 0.11 0.649 −0.98 −0.67 −0.31 0.181 −0.77 −0.84 0.17 0.778
Recognizing faces 0.86 0.78 0.08 0.724 0.90 0.77 0.13 0.561 1.13 0.55 0.58 0.029
Seeing prices when shopping −0.27 −0.43 0.16 0.486 −0.43 −0.27 −0.15 0.498 −0.46 −0.34 −0.12 0.626
Walk on uneven ground 0.34 0.39 −0.05 0.815 0.53 0.18 0.35 0.118 0.45 0.22 0.23 0.369
Needlework and handicraft 0.06 0.03 0.02 0.916 0.03 0.03 0.00 >0.995 0.07 0.23 −0.16 0.551
Reading text on TV −0.01 0.20 −0.20 0.382 −0.03 0.15 −0.18 0.432 0.11 0.21 −0.10 0.685
Hobbies 0.85 0.78 0.07 0.772 0.87 0.78 0.08 0.712 0.72 0.82 −0.10 0.717
Chinese n= 70 131    93 109    79 96   
Daily-life activities in general −0.01 0.28 −0.29 0.299 0.36 0.04 0.32 0.230 −0.03 0.24 −0.26 0.360
Satisfaction with vision −2.19 −1.98 −0.21 0.465 −2.16 −1.95 −0.21 0.443 −2.12 −2.05 −0.07 0.809
Reading newspaper −0.73 −0.64 −0.09 0.748 −0.54 −0.77 0.23 0.377 −0.66 −0.61 −0.05 0.856
Recognizing faces 1.30 1.13 0.17 0.568 0.92 1.40 −0.48 0.086 1.44 1.02 0.42 0.163
Seeing prices when shopping −0.71 −0.67 −0.04 0.895 −0.79 −0.56 −0.23 0.384 −0.57 −0.67 0.10 0.724
Walk on uneven ground 1.12 1.12 0.00 >0.995 1.17 1.09 0.08 0.760 0.98 1.21 −0.23 0.439
Needlework and handicraft 0.14 0.11 0.03 0.927 0.25 −0.01 0.26 0.345 0.04 0.28 −0.24 0.419
Reading text on TV 0.21 −0.12 0.32 0.259 −0.01 −0.01 0.00 >0.995 0.17 −0.13 0.30 0.300
Hobbies 0.89 0.75 0.14 0.635 0.81 0.79 0.02 0.942 0.79 0.71 0.08 0.793
  1. aWelch’s test