Quantification of the whole-body burden of radiographic osteoarthritis using factor analysis

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.

ISSN: 1478-6362