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Table 2 Results of factor loading and fit indexes of Confirmatory Factor Analysis of the WOMAC short questionnaire in both cohorts

From: Validation of a proposed WOMAC short form for patients with hip osteoarthritis

Items*

Item description

Cohort 1

(n = 788)

Cohort 2

(n = 445)

  

Pain

Function

Pain

Function

Pain item 1

Walking on flat surface

0.75

-

0.77

-

Pain item 2

Up/down stairs

0.84

-

0.84

-

Pain item 4

Sitting or lying

0.53

-

0.59

-

Function item 1

Descending stairs

-

0.74

-

0.74

Function item 2

Ascending stairs

-

0.74

-

0.77

Function item 3

Rising from sitting

-

0.67

-

0.67

Function item 6

Walking on flat surface

-

0.69

-

0.72

Function item 7

Getting in/out of a car

-

0.67

-

0.71

Function item 8

Shopping

-

0.71

-

0.70

Function item 9

Putting on socks

-

0.55

-

0.53

Function item 15

Getting on/off toilet

-

0.66

-

0.67

χ2 (df)

 

226.11 (40)

119.97 (40)

RMSEA

 

0.0792

0.0690

CFI

 

0.9539

0.9650

NNFI

 

0.9366

0.9518

  1. *Items are referred to by the original name in the WOMAC long form.
  2. df = degrees of freedom; RMSEA = root mean square error of approximation; CFI = comparative fit index; NNFI = non-normed fit index.
  3. Correlation between the two latent factors (pain and function) is set to be different from 0, therefore both latent factors are specified to be intercorrelated. The estimation of the correlation coefficient was 0.89 in the first cohort and 0.82 in the second one.
  4. Covariance was specified between the error items of the following three pair of items: "Pain walking on flat surface" and "functional limitation walking on flat surface", "pain up/down stairs" and "functional limitation ascending stairs", and "functional limitation getting in/out of a car" and "functional limitation putting on socks".