Survey modes comparison in contingent valuation: Internet panels and mail surveys.

Stated preferences methods are extensively applied in health economics to elicit preferences. Although mailed surveys were commonly used to collect data, internet panel (IP) surveys are being increasingly used. This raises questions about the validity of responses and estimated willingness-to-pay (WTP) values generated from IP surveys. We conduct the first study in health to compare a contingent valuation IP survey with a mailed survey using the electoral roll. Our IP has a higher response rate and lower item missing response rate. The difference is reduced but remains when restricting comparisons with valid WTPs. Sample characteristics differ, with significant differences between modes for gender, age, income, and attitudes and knowledge. Although difference in WTP values exist, with the IP resulting in higher values, we find limited evidence that such differences are statistically significant. The mail survey has lower initial cost per response; however, once restricting samples to valid WTP responses with nonmissing respondent information, the cost per response across modes is similar. Our results, suggesting that IPs generate valid and cost-effective values, are encouraging as researchers move increasingly to IPs to collect preference data.