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Table 3 Differential item functioning (DIF) and differential bundle functioning (DBF) results

From: Validation of a mobility item bank for older patients in primary care

 

Item Wording

 

External criteria

Internal criterion

PF-10

SPPB

Beta

p

Beta

p

Beta

p

Walking (W)

W01

Walk around the house

-.01

.75

-.02

.41

-.03

.32

W02

Walk without losing balance

.02

.56

.03

.38

.01

.71

W03

Walk without tripping

.05

.13

.07

.03

.07

.07

W04

Walk outdoors

-.06

.06

-.05

.25

-.08

.07

W05

Walk 5 minutes nonstop

-.04

.23

-.03

.40

-.05

.19

W06

Cross the road

.04

.06

.05

.11

.01

.82

W07

Walk 1 kilometre with rests

-.08

.07

-.04

.43

-.11

.03

W08

Walk on a slippery surface

.01

.80

.06

.19

.01

.87

W09

Walk 15 minutes nonstop

-.07

.08

-.09

.04

-.12

.02

W10

Walk 5 minutes at a fast pace

.14

.01

-.11

.05

-.14

.01

W11

Walk 2 kilometres nonstop

-.21

.00

-.14

.01

-.17

.00

W12

Walk several kilometres on uneven ground

-.03

.58

.04

.40

-.01

.93

W13

Walk half an hour at a fast pace nonstop

-.14

.01

-.04

.50

-.07

.30

W14

Climb a steep hill

-.02

.59

.07

.07

.09

.06

W15

Run a short distance

-.05

.05

.02

.68

-.01

.91

W16

Run one and a half kilometres

-.08

.06

.04

.43

.02

.71

 

 DBF

  

-.14

 

-.58

 
 

 Average DBF (DBF/n items)

  

-.01

 

-.04

 

Up and down stairs (UDS)

UDS01

Climb 4 or 5 steps, using handrails

.05

.09

.03

.28

.05

.19

UDS02

Step up and down from a curb

.01

.76

.06

.09

.02

.58

UDS03

Climb 4 or 5 steps, without handrails

.06

.18

.10

.05

.06

.30

UDS04

Go down 4 or 5 steps, using handrails

.05

.11

.04

.17

.03

.34

UDS05

Get on and off a bus

.05

.17

.11

.01

.06

.14

UDS06

Go down 4 or 5 steps, without handrails

.06

.15

.13

.01

.10

.07

UDS07

Go up 1 flight of stairs, without handrails

.02

.74

.10

.06

.08

.19

UDS08

Go down 1 flight of stairs, using handrails

.05

.11

.06

.07

.06

.10

UDS09

Climb stairs carrying little weight

-.05

.17

-.04

.29

-.02

.61

UDS10

Go up 3 flights of stairs, using handrails

.02

.60

.06

.13

.07

.14

UDS11

Go down 3 flights of stairs, using handrails

.01

.70

.03

.42

.05

.32

 

 DBF

  

.68

 

.56

 
 

 Average DBF (DBF/n items)

  

.06

 

.05

 

Body Position (BP)

BP01

Get into bed†

-

-

-

-

-

-

BP02

Turn over in bed

.01

.91

.05

.29

.06

.15

BP03

Sit down on a couch

.02

.50

.05

.16

.02

.54

BP04

Sitting, bend over to pick something up

-.04

.32

-.02

.66

.01

.81

BP05

Remain seated for 10 minutes without back rest

.07

.05

.13

.00

.16

.00

BP06

Sit up in bed, being lied down

-.03

.47

-.01

.74

-.00

.97

BP07

Sit down and stand up from a chair†

-

-

-

-

-

-

BP08

Stand up from a low, soft couch

.10

.03

.09

.04

.08

.11

BP09

Pick up a chair†

-

-

-

-

-

-

BP10

Reach overhead while standing

.19

.00

.22

.00

.26

.00

BP11

Turn around while standing

.07

.09

.08

.04

.09

.04

BP12

Remain standing for 10 minutes

-.03

.50

-.01

.83

.00

.98

BP13

Standing, bend down to pick something up

-.04

.37

.01

.80

.01

.80

BP14

Get up from the floor from lying on your back

.20

.00

.24

.00

.23

.00

BP15

Kneel down

.29

.00

.32

.00

.32

.00

BP16

Get into and out of a car

.03

.53

.08

.06

.08

.06

 

 DBF

  

1.23

 

1.32

 
 

 Average DBF (DBF/n items)

  

.09

 

.10

 

Carrying, Lifting and Pushing (CLP)

CLP01

Push or pull a large object

.07

.09

.12

.01

.13

.01

CLP02

Move or drag a bed

.11

.02

.13

.00

.16

.00

CLP03

Lift 4 or 5 kg from the floor

.17

.00

.22

.00

.25

.00

CLP04

Turn over a mattress

.10

.04

.14

.00

.18

.00

CLP05

Change gas bottle

.23

.00

.22

.00

.23

.00

 

 DBF

  

.83

 

.95

 
 

 Average DBF (DBF/n items)

  

.17

 

.19

 
  1. DIF: in bold, significant values p < 0.002; DBF: in bold, significant values p < 0.01.
  2. † Items excluded after Testgraf analysis.