It's not just what you do, it's the way that you do it: the effect of different payment card formats and survey administration on willingness to pay for health gain.

A general population sample of 314 Australian respondents were randomly allocated to complete a contingent valuation survey administered by face-to-face or telephone ('phone-mail-phone') interview. Although the telephone interview was quicker to complete, no significant difference was found in values obtained through either method. Within each sub-sample, respondents were also randomly allocated to the three different versions of the payment card (PC) questionnaire format: values listed from high-to-low, values listed from low-to-high and values randomly shuffled. The high-to-low version resulted in significantly higher values than the other versions. Further analyses indicate that the randomly shuffled PC version may produce the most 'valid' values