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 cultureconfirmed
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$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$28.4) for children is similar to
a lower bound estimate of WTP (2002 PPP adjusted US$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.