To analyze correlational validity of self-report responses regarding patient preference between 2 drugs at the conclusion of a crossover double-blind clinical trial in patients with osteoarthritis (OA) of the knee or hip.
Patients were randomized to 6 weeks' treatment of diclofenac/misoprostol or acetaminophen, followed by crossover to 6 weeks of the other drug. Patient preference was queried at the final visit: "Please compare control of your arthritis during the first and second periods as 'much better' or 'better' in the first period, 'no different' or 'better' or 'much better' in the second period." Patient preference ratings were evaluated in comparisons with 4 independent self-report measures within each treatment period: (1) change in Western Ontario McMaster (WOMAC) questionnaire scores; (2) change in pain visual analog scale (VAS) on a multidimensional Health Assessment Questionnaire (MDHAQ); (3) patient ratings of drug efficacy; and (4) patient report of change in arthritis status, as well as investigator ratings of the more efficacious drug.
Among 173 patients, diclofenac/misoprostol was rated as "much better" by 54 and "better" by 45, acetaminophen was rated as "better" by 18 and "much better" by 17, and "no difference" by 39 patients. Spearman rank correlations for patient preferences were significant for changes in WOMAC scores, pain VAS, and independent patient ratings of drug efficacy and changes in arthritis status within each treatment period, as well as with physician ratings of the more efficacious drug (p < 0.001).
Significant correlational validity is documented for patient self-report of preferences between 2 drugs compared to independent measures within each treatment period in this crossover clinical trial in patients with OA of the knee or hip.