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Table 3 DIF analysis: CHI SQUARE values for overall DIF (model 3-model1) with uniform and non-uniform DIF identified

From: Exploring differential item functioning in the SF-36 by demographic, clinical, psychological and social factors in an osteoarthritis population

Item Age Gender Social class Social deprivation Employ Mood BMI No. joints Hip/Knee
Physical functioning          
PF1 vigorous activities 19.21 NU 2.26 1.26 5.24 3.99 0.23 13.80 NU 0.99 0.93
PF2 moderate activities 1.98 1.32 5.90 5.15 1.47 3.93 0.21 4.77 1.50
PF3 lift/carry groceries 0.53 29.08 U * 1.13 0.39 2.40 1.90 1.03 2.53 2.98
PF4 several flight stairs 1.96 10.17 4.24 5.17 5.14 4.94 2.13 3.00 5.63
PF5 one flight stairs 2.87 0.49 2.33 1.91 0.79 0.54 3.31 1.44 1.67
PF6 bend/knee/stoop 16.73 NU 5.58 4.74 2.31 4.42 1.21 5.43 1.024 0.21
PF7 walk more mile 4.04 2.63 2.85 0.92 2.75 2.09 0.85 1.39 0.65
PF8 walk half mile 0.37 0.41 3.37 3.01 1.02 1.48 0.50 0.57 7.25
PF9 walk 100 yards 10.73 0.20 2.87 6.53 0.00 3.01 2.40 4.07 0.81
PF10 bathing or dressing 1.01 4.36 2.04 3.71 11.01 12.67 6.26 1.80 1.49
Pain          
P1 intensity of bodily pain 8.55 0.24 8.21 1.60 32.45 NU * 4.65 4.10 0.73 4.59
P2 extent pain interfere normal work 5.78 7.66 10.34 U/NU * 5.0 10.27 5.92 2.05 0.99 7.18
Role physical          
RP1 cut down time on work/act. 1.74 0.63 4.20 10.26 NU * 17.13 NU * 0.44 0.05 2.65 9.18 NU
RP2 accomplished less 10.98 U 1.05 1.43 0.89 0.72 0.48 0.44 2.55 4.14
RP3 limited in kind of work/activities 1.58 2.08 1.75 3.62 0.72 8.57 0.28 6.54 0.16
RP4 difficulty performing work/act. 2.10 1.69 2.80 1.04 10.52 U 5.42 0.15 1.26 0.80
Social functioning          
SF1 interferes with social activities 14.95 NU 3.82 9.05 0.87 19.50 NU * 0.43 1.71 0.74 1.46
SF2 time interferes with social act. 9.67 9.57 1.33 5.95 7.16 4.80 1.83 0.22 4.78
Role emotional          
RE1 cut down time work/activities 0.42 0.25 5.75 1.40 1.14 0.12 1.03 0.32 0.97
RE2 accomplished less 6.68 0.35 0.18 2.00 6.45 4.06 3.46 5.45 9.32 *
Not as careful work/activities 6.94 1.15 1.66 2.30 2.66 5.00 4.85 4.21 0.97
Mental          
MH1 nervous 3.05 14.50 U * 4.19 0.74 5.40 18.11 NU * 1.53 4.24 2.31
MH2 down in dumps 4.14 0.98 12.31 U * 0.65 0.95 7.28 6.96 2.32 1.24
MH3 calm and peaceful 8.48 6.54 1.23 4.00 6.36 46.33 NU * 11.48 4.63 9.75
MH4 downhearted and low 2.39 1.11 4.13 10.24 5.09 14.35 NU * 8.22 0.02 1.29
MH5 happy person 0.93 1.64 8.36 3.18 9.18 47.19 NU * 3.82 0.27 2.60
Vitality          
V1 full of life 6.93 0.16 3.25 7.25 4.56 7.48 3.09 4.95 0.28
V2 energy 10.91 U 0.36 0.17 1.10 1.67 5.35 2.57 2.70 0.44
V3 worn out 8.82 U 0.33 0.05 3.25 10.45 U 0.34 1.68 4.38 0.45
V4 tired 5.49 8.19 2.48 2.20 7.07 2.59 0.20 0.91 0.88
General health          
GH1 health in general 9.12 2.30 6.04 2.21 8.77 3.05 1.49 2.48 2.66
GH2 get ill more easily than others 2.26 3.70 1.01 6.64 1.39 12.03 U * 1.62 3.71 3.16
GH3 as healthy as anybody I know 2.47 5.74 6.31 2.51 5.02 3.97 2.41 2.10 0.26
GH4 except health to get worse 4.36 10.26 6.61 10.71 4.47 3.46 1.68 4.12 2.41
GH5 my health is excellent 0.94 1.05 0.91 2.49 1.10 9.85 2.77 7.90 0.23
  1. Where the item has been dichotomised, the larger value is entered in the table.
  2. KEY: U = uniform. NU = non-uniform, * = still significant after adjusting for age.
  3. Boldface=significant DIF.