Table 2

Factor analysis: principal component analysis using Varimax rotation

Component (Eigenvalue)
1 (5.33)2 (1.91)3 (1.62)4 (1.15)5 (0.99)6 (0.94)
 Anti-CCP (0, 1, 2)*0.1040.0640.0350.0790.0940.878
 Rheumatoid factor (0, 1, 2)*0.1050.0130.0640.0530.1170.878
Acute phase measures
 CRP (0, 1, 2)*–0.0040.101–0.0490.8470.0040.055
 ESR (tertiles)0.0120.026–0.0420.847–0.0420.121
Functional measures
 HAQ (tertiles)0.1030.1800.3430.5550.062–0.074
Joint swelling
 SJC (1, 2–6, 7–28)0.6120.3560.1980.0750.5260.125
 MCP swelling (yes/no)0.8390.1030.2820.0170.1490.158
 PIP swelling (yes/no)0.2870.1380.082–0.0030.8520.176
 Wrist swelling (yes/no)0.1650.8650.1400.1190.0550.102
 MTP swelling (yes/no)0.0550.0470.0240.0090.0220.127
Joint tenderness
 Tender joint count (1, 2–6, 7–28)0.2680.2040.7670.0580.3840.047
 MCP tenderness (yes/no)0.5090.0140.723–0.0030.1080.094
 PIP tenderness (yes/no)0.1030.0450.550–0.0480.7100.098
 Wrist tenderness (yes/no)0.0010.6580.5990.0360.0010.048
Symmetry of joint involvement
 Symmetrical MCP swelling0.8260.2050.0950.0390.1630.062
 Symmetrical wrist swelling0.2290.785–0.0240.1330.194–0.037
 ThemeMCP involvementWrist involvementHand/finger tendernessAcute phase responsePIP involvementSerology
 Test variable for subsequent analysisMCP swellingWrist swellingPIP or MCP or wrist tendernessCRP or ESR (low/mod/high)PIP swellingAnti-CCP or ESR (low/mod/high)
  • * Categories defined as follows: 0, normal by local standards; 1, below the median of non-normal values; 2, above the median of non-normal values.

  • anti-CCP, anti-cyclic citrullinated protein; CRP, C reactive protein; ESR, erythrocyte sedimentation rate; HAQ, Health Assessment Questionnaire; MCP, metacarpophalangeal; MTP, metatarsophalangeal; PIP, proximal interphalangeal; SJC, swollen joint count.

  • Loadings of >0.6 are highlighted in bold to facilitate the interpretation.