Assessment of the Psychometric Properties of the Danish VISA-P

Table 4

Multivariable regression analysis for all subject of differential item functioning (DIF) on the covariates sex, duration of symptoms, body mass index (BMI), and age group.

Item 1

Item 2

Item 3

Item 4

Item 5

Item 6

Item 7

Item 8

DIF (95% CI)

-value

DIF (95% CI)

-value

DIF (95% CI)

-value

DIF (95% CI)

-value

DIF (95% CI)

-value

DIF (95% CI)

-value

DIF (95% CI)

-value

DIF (95% CI)

-value

Sex

0.380

0.624

0.665

0.968

0.948

0.071

0.646

0.658

Male

Ref

Ref

ref

ref

ref

ref

ref

ref

Female

−0.35 (−1.12; 0.43)

0.379

−0.10 (−0.52; 0.31)

0.624

−0.10 (−0.56; 0.36)

0.665

−0.01 (−0.48; 0.46)

0.968

0.02 (−0.49; 0.53)

0.948

0.42 (−0.04; 0.88)

0.071

−0.16 (−0.87; 0.54)

0.646

0.29 (−0.98; 1.56)

0.658

Duration (months)

0.915

0.002

0.158

0.179

0.005

0.142

<.0001

0.008

No Sympt

Ref

Ref

ref

ref

ref

ref

ref

ref

<3

0.49 (−0.86; 1.84)

0.474

−1.07 (−1.79; −0.34)

0.004

−0.22 (−1.03; 0.58)

0.584

−0.53 (−1.35; 0.28)

0.202

1.35 (0.47; 2.24)

0.003

−0.19 (−0.99; 0.61)

0.647

3.81 (2.59; 5.04)

<.0001

−3.65 (−5.86; −1.45)

0.001

4–12

0.39 (−1.03; 1.81)

0.589

−1.20 (−1.97; −0.44)

0.002

0.42 (−0.43; 1.27)

0.331

−0.33 (−1.19; 0.53)

0.452

1.53 (0.59; 2.46)

0.001

0.47 (−0.38; 1.31)

0.279

2.64 (1.35; 3.93)

<.0001

−3.91 (−6.23; −1.58)

0.001

>12

0.34 (−1.13; 1.82)

0.649

−0.46 (−1.25; 0.34)

0.257

0.19 (−0.69; 1.07)

0.665

−0.87 (−1.76; 0.03)

0.058

0.81 (−0.16; 1.78)

0.102

0.26 (−0.61; 1.14)

0.556

3.20 (1.86; 4.54)

<.0001

−3.49 (−5.91; −1.07)

0.005

BMI (kg/m^2)

0.459

0.267

0.769

0.176

0.003

0.734

0.783

<25

Ref

Ref

ref

ref

ref

ref

ref

Ref

>25

−0.27 (−0.98; 0.44)

0.459

−0.22 (−0.60; 0.17)

0.267

0.06 (−0.36; 0.49)

0.769

−0.30 (−0.73; 0.13)

0.175

−0.70 (−1.17; 0.23)

0.003

0.07 (−0.35; 0.49)

0.734

−0.09 (−0.73; 0.55)

0.783

1.43 (0.27; 2.59)

0.015

Age (years)

0.946

0.589

0.799

0.403

0.360

0.173

0.040

0.733

≤30

Ref

Ref

ref

ref

ref

ref

ref

ref

≥30

0.02 (−0.62; 0.67)

0.946

0.10 (−0.25; 0.44)

0.589

0.05 (−0.33; 0.43)

0.799

0.17 (−0.22; 0.56)

0.402

0.20 (−0.23; 0.62)

0.359

0.27 (−0.12; 0.65)

0.172

−0.62 (−1.2; −0.03)

0.039

−1.18 (−1.24; 0.87)

0.733

The results show considerable DIF for all items. indicate DIF remains (only for Item 8 for BMI) when healthy people are omitted from the analysis.