Comparison of cost-of-illness with willingness-to-pay estimates to avoid shigellosis: evidence from China.

Previous studies have shown that cost of illness (COI) measures are lower than the conceptually correct willingness-to-pay (WTP) measure of the economic benefits of disease prevention. We compare COI with stated preference estimates of WTP associated with shigellosis in a rural area of China. COI data were collected through face-to-face interviews at 7 and 14 days after culture-confirmed diagnosis. WTP to avoid an episode similar to the one the respondent just experienced was elicited using a sliding-scale payment card. In contrast to previous studies' findings, average COI estimates (2002 PPP adjusted US dollars 28.2) approximate an upper bound estimate of WTP, rather than a lower bound. One explanation for the similarity between COI and WTP is that preventive expenditures and disutility due to pain and suffering are low for shigellosis. WTP to avoid additional cases in children aged 0-5 years is higher than in adults. Also, average COI (2002 PPP adjusted US dollars 28.4) for children is similar to a lower bound estimate of WTP (2002 PPP adjusted US dollars 16.4) and lies within the WTP range. Because the monetary loss associated with another episode in children is small, caregivers' higher WTP may be attributable to the disutility of illness due to the children's pain and suffering. These findings suggest that for some diseases, COI may approximate more comprehensive measures of economic benefits.