Varimax rotation of four component (1–4) solution for PsA disease activity items. The loading of each variable on the four components is shown.

BASDAI, Bath Ankylosing Spondylitis Disease Activity Index; CRP, C-reactive protein; ESR, erythrocyte sedimentation rate; HAQ, health assessment questionnaire; PASI, psoriasis area and severity index; SF-36 MCS, Short Form-36 health survey Mental Components Summary; SJC, swollen joint count; TJC, tender joint count; VAS PAIN, visual analogue scale patient pain assessment; VAS PtGA, visual analogue scale patient global disease activity assessment.