Classification criteria for psoriatic arthritis: Development of new criteria from a large international study

To compare the accuracy of existing classification criteria for the diagnosis of psoriatic arthritis (PsA) and to construct new criteria from observed data.

Data were collected prospectively from consecutive clinic attendees with PsA and other inflammatory arthropathies. Subjects were classified by each of 7 criteria. Sensitivity and specificity were compared using conditional logistic regression analysis. Latent class analysis was used to calculate criteria accuracy in order to confirm the validity of clinical diagnosis as the gold standard definition of "case"-ness. Classification and Regression Trees methodology and logistic regression were used to identify items for new criteria, which were then constructed using a receiver operating characteristic curve.