Table 2 Rasch analyses of dimensionality and differential item functioning (DIF^a) for WG-SS, ADL, and IADL items (recoded as binary variables, limited vs non-limited) (HSM survey)

WG-SS items

Fit with the one-dimensional Rasch model

Differential Item Functioning

Overall fit p-value = 0.88, Person separation index = 0.60

location

Chi square

P-value

Uniform DIF

Non-Uniform DIF

Seeing

0.30

1.16

0.88

–

–

Hearing

-0.21

0.69

0.95

–

–

Washing and dressing

1.04

5.53

0.24

age

–

Walking or climbing steps

-0.88

4.57

0.33

age

–

Remembering or concentrating

-1.27

0.53

0.97

–

–

Communicating

1.01

3.53

0.47

gender, age, occupation

–

ADL items

Fit with the one-dimensional Rasch model

Differential Item Functioning

Overall fit p-value < 0.0000001, Person separation index = 0.83

location

Chi square

P-value

Uniform DIF

Non-Uniform DIF

Feeding

3.56

2.61

0.46

–

–

Toileting

0.05

7.20

0.07

–

–

Dressing

-0.98

18.34

0.0004

–

–

Bathing

2.09

2.86

0.41

–

–

Transferring from bed or chair

-1.26

23.55

0.00003

–

–

Walking

-3.45

28.70

0.000003

–

–

IADL items

Fit with the one-dimensional Rasch model

Differential Item Functioning

Overall fit p-value = 0.0003, Person separation index = 0.87

location

Chi square

P-value

Uniform DIF

Non-Uniform DIF

Shopping

-1.17

10.53

0.03

–

–

Preparing meals

0.96

14.82

0.01

gender

–

Doing light housework

-0.67

9.91

0.04

gender

–

Doing heavy housework

-1.32

2.03

0.73

–

–

Handling finances

-0.51

9.60

0.05

education

–

Using telephone

2.71

8.76

0.07

–

–