Comparing willingness‐to‐pay and time‐trade‐off as the measures of burden of psoriasis: A pooled analysis of community, hospital, and web‐based samples in China

Abstract

Willingness-to-pay (WTP) and time-trade-off (TTO) are widely used as measures of disease burden. However, the sensitivity of the metrics has not been compared in psoriasis. This article aims to report WTP and TTO in Chinese psoriasis patients, and to compare the WTPcure (USD), WTPcontrol (%), and TTO regarding the sensitivity in measuring the burden of psoriasis. Patients were recruited from a community-based cohort, a tertiary hospital, and an online forum. WTP was elicited for two scenarios: WTP for controlling the disease and WTP for curing the disease. WTPcontrol was elicited by asking about the percentage of monthly income that the participant patients would like to pay to fully control the clinical symptoms of psoriasis and WTPcure was elicited as absolute money for curing the disease. The evaluation of WTP and TTO were referred to the Psoriasis Area and Severity Index (PASI) as the indicator of clinical severity, and the Dermatology Life Quality Index (DLQI) as the measure of impaired quality-of-life. Data distribution, concurrent validity, and capability of discriminating moderate-to-severe psoriasis (receiver operating characteristic curve, ROC) were compared among the indices. A total of 479 patients were enrolled from the cohort (88), hospital (175), and web (216). WTPcontrol was significantly higher in patients with PASI>10 than those with PASI<10, while TTO was significantly higher in patients with DLQI>10 than those with DLQI<10. WTP control showed a positive association with PASI in mild psoriasis (r=0.36, p < 0.001), while TTO showed an inverse correlation to DLQI in different severity subgroups, respectively (r=-0.20, p=0.001). ROC analysis showed consistent results that WTP control was superior in discriminating patients with PASI>10, while WTP control was better in discriminating DLQI>10. WTPcure demonstrated no significant results. WTPcontrol is superior in detecting mild psoriasis compared to TTO, while TTO is more sensitive in measuring the impaired QoL.