Survey: 3,000; Experiment: 894,791
We removed all individuals who (1) were listed as inactive, (2) lacked a valid current Connecticut mailing address (including failing to pass a National Change of Address [NCOA] filter), or (3) had their mail delivered to a post office box. Similarly, we eliminated any voter who voted by absentee ballot in 2006, 2008, or 2010 because many of these individuals may have already voted at the time the mailing was sent. We also removed any registrants less than 18 years of age or over the age of 85. Finally, we removed records from households with more than five registrants at a single address because these individuals are likely to live in temporary (e.g., school dorms) or group housing where mail would be less likely to be delivered on time or where the registrant is more likely to have moved. From this pool of eligible registrants, if there were multiple eligible registrants from a single household (address), we randomly selected a single registrant.
We identified our three experimental strata and assigned treatments. Within each stratum, randomization took place within blocks (constant proportions for all blocks within the group, and leftovers [groupings too small to be blocked] were independently randomly assigned with the same target proportions). See the supporting information for complete details.
Six of our seven treatment letters appeared on Secretary of State letterhead (full text of all letters appears in the supporting information): SOS Secrecy 1 (Anonymity), SOS Secrecy 2 (No Intimidation), SOS Secrecy Combined, SOS Short, SOS Control, SOS Civic Duty, and Generic Civic Duty.