Contribution of individual variables to composite scores. Explanation of score variability for (a) the Simplified Disease Activity Index (SDAI), (b) the Disease Activity Score (DAS)28, and (c) the DAS28-CRP for the respective clinical and acute phase reactant (APR) variables, at zero-order (i.e. R2 if the variable was introduced as the first one; black bars) or finally (i.e. R2 if variable was introduced in the model as the last one; grey bars), and item colinearity within the respective composite index (1 - tolerance, expressed as percentage; white bars; n = 767). CRP, C-reactive protein; ESR, erythrocyte sedimentation rate; PGA/EGA, patient/evaluator global assessment of disease activity (100 mm visual analogue scale); TJC/SJC, tender/swollen joint count (28 joints).