For each advertisement, we specified a daily budget (range $5�C$20) and a maximum bid we would be willing to make for each auction, which were adjusted throughout the 6-month campaign selleck catalog based on recruitment rates and costs. SSI: We launched an E-mail campaign through SSI, an online sampling service that recruits and maintains a panel of individuals who have indicated that they are willing to complete online surveys. SSI authenticates registered respondents to avoid duplicate survey entries and misrepresentation and allows for targeting by age and various behavioral characteristics, including smoking status. While a fee is traditionally charged to pay each respondent for their participation, SSI agreed to forgo this extra charge and allow project staff to conduct a drawing for prizes as approved by our IRB.

For the present study, young adults registered with SSI were sent an E-mail invitation for our online survey of tobacco use for a chance to win a prize. We incurred a charge of $19.24 for each completed survey and no charge for any incomplete responses through this process. Text of the E-mailed invitations was similar to the Craigslist ads, including a first line that read: Do you smoke cigarettes? mention of a UC San Francisco research study, and the chance to win a raffle prize worth either $25 or $400. Evaluation of recruitment methods We used various criteria to evaluate our recruitment methods. First, number of views of the survey was tracked through both the Internet advertising campaign and the survey sampling company but not through Craigslist.

In addition, during the screening and enrollment process, each user was asked to indicate how they heard about our survey. Options included (a) survey sampling company, (b) Craigslist, (c) Facebook, (d) MySpace, (e) another social networking site, (f) a friend told me about it, and (g) ��other.�� From this, we were able to track the proportion of individuals by recruitment method that reached the survey, signed consent, met survey criteria, and completed the survey. Second, number of invalid responses was tracked, including those due to inconsistent data (e.g., birthdate did not match age) or duplicate IP addresses that had an ineligible entry and then repeat entry. Third, average cost per registered participant was computed for each method by totaling all the recruitment costs associated with using the method and dividing by the number of participants whose eligible status or completion status could be directly attributed to that method. Fourth, for Internet Brefeldin_A advertisements, we determined which Web sites and the types of advertisements (banner or text) were most effective at recruiting eligible participants and those who completed the survey in entirety.