Primary Outcomes (end points)
Before canvassers went into the field, the study first gathered baseline
positions on a range of political attitudes for all participants using an ostensibly unrelated online
survey. The survey included 50 questions, as described in the Supplemental Online Materials (SOM).
The two questions concerning same-sex marriage and feelings about gay people were buried amid
a large number of items on unrelated topics so that respondents would not suspect any connection
between the survey and the canvassing visit. The panel survey included the two outcome measures in
every wave, but the overall content of the survey was kept fresh by randomly rotating new questions
in each wave. Another important feature of the design concerns blinding of canvassers and survey
respondents. Voters were unaware that the online survey was related to the canvassing effort, and
canvassers had no knowledge that voters were participants in an online survey. Finally, to prevent
housemates from completing each other’s surveys, extensive precautions were taken, including issuing distinct personal login instructions to take differently named surveys, tracking of distinct IP addresses
and session cookies, and sending invitations to take the survey during working hours (91% were in
fact completed at work), when housemates would be less likely to be together.