Table 2.

Correlation among instruments in a cross-sectional setting.

N of RAPID3 /instrumentRAPID3PsAID12SF-12 PCSSF-12 MCSBASDAIFACIT-FWLQPhys GlobalPhys ArthSwollen JointsTender JointsPain
PsAID122070.90*
PsAID92070.90*1.00*
SF-12 PCS270−0.67*−0.73*
SF-12 MCS270−0.41*−0.48*0.11
BASDAI2050.88*0.87*−0.68*−0.42*
FACIT-F188−0.77*−0.84*0.71*0.54*−0.78*
WLQ**1410.67*0.72*−0.63*−0.50*0.68*−0.76*
Phys Global3040.63*0.63*−0.50*−0.26*0.56*−0.48*0.45*
Phys Arth3060.60*0.56*−0.45*−0.22*0.49*−0.42*0.38*0.84*
Swollen Joints2310.39*0.39*−0.28*−0.17*0.34*−0.26*0.25*0.54*0.68*
Tender Joints2310.42*0.37*−0.33*−0.15*0.35*−0.28*0.29*0.55*0.63*0.77*
Pain3440.94*0.89*−0.63*−0.34*0.85−0.720.620.640.610.390.41
Global3430.93*0.83*−0.62*−0.42*0.81−0.720.640.560.550.350.380.83*
  • Spearman correlation coefficients are shown here. Yellow indicates a strong correlation (rho 0.8–1.0) and blue a moderate correlation (0.6–0.79).

  • * p < 0.05.

  • ** The productivity score of the Work Limitations Questionnaire (WLQ) is shown here. The WLQ index had nearly identical coefficients. Numbers in italics: Pain and global assessment are part of the RAPID3, so the correlation is expected to be high. Note that the additional columns with the other outcomes were not part of the original hypotheses. RAPID3: Routine Assessment of Patient Index Data 3; PsAID12: Psoriatic Arthritis Impact of Disease 12-question version; PsAID9: Psoriatic Arthritis Impact of Disease 9-question version; SF-12 PCS: Medical Outcomes Study Short Form-12 physical component summary; SF-12 MCS: SF-12 mental component summary; BASDAI: Bath Ankylosing Spondylitis Disease Activity Index; FACIT-F: Functional Assessment of Chronic Illness Therapy Fatigue scale; Phys global and Phys arth: physician global assessments for overall health and arthritis, respectively.