Table 4

Cronbach's alpha (internal consistency reliability) and average inter-variable correlation for the 4 factors

Factor*

n (obs)

n (variables)

Cronbach's alpha

Average inter-variable correlation


IP/CMC

2047

20

0.95

0.51

MCP

2081

8

0.81

0.35

Knee

1451

4

0.85

0.59

Spine

1917

10

0.80

0.29


*IP/CMC factor: Thumb IP, DIP 2-5, PIP 2-5, CMC1; MCP factor: MCP 2-5, Knee factor: TFJ and PFJ; Spine factor: Disc space narrowing and osteophytes L1/2 to L5/S1.

Number of observations with data for a factor

Number of radiographic variables included in a factor

CMC, carpometacarpal joint; DIP, distal interphalangeal joint; IP, interphalangeal joint; MCP, metacarpophalangeal joint; PFJ, patellofemoral joint; PIP, proximal interphalangeal joint; TFJ, tibiofemoral joint.

Nelson et al. Arthritis Research & Therapy 2011 13:R176   doi:10.1186/ar3501

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