January 7, 2016

Can Likely Voter Models Be Improved?

Methodology

The American Trends Panel surveys (ATP)

The American Trends Panel (ATP), created by Pew Research Center, is a nationally representative panel of randomly selected U.S. adults living in households. Respondents who self-identify as internet users (representing 89% of U.S. adults) participate in the panel via monthly self-administered Web surveys, and those who do not use the internet participate via telephone or mail. The panel is being managed by Abt SRBI.

Data in this report are drawn from two waves of the panel, September and November. The September wave was conducted Sept. 9-Oct. 3, 2014, among 3,154 respondents (2,811 by Web and 343 by mail). The November wave was conducted Nov. 17-Dec. 15, 2014, among 3,212 respondents (2,856 by Web and 356 by mail). For the purpose of this report, respondents are included only if they responded to both the September and November waves of the panel, told us they were registered to vote, and were able to be matched to the national voter file (a total of 2,424 respondents). The margin of sampling error for the full sample of 2,424 respondents is plus or minus 2.3 percentage points.

All current members of the American Trends Panel were originally recruited from the 2014 Survey of Political Polarization, a large (n=10,013) national landline and cellphone random digit dial (RDD) survey conducted Jan. 23 to March 16, 2014, in English and Spanish. At the end of that survey, respondents were invited to join the panel. The invitation was extended to all respondents who use the internet (from any location) and a random subsample of respondents who do not use the internet.9

Of the 10,013 adults interviewed, 9,809 were invited to take part in the panel. A total of 5,338 agreed to participate and provided either a mailing address or an email address to which a welcome packet, a monetary incentive and future survey invitations could be sent. Panelists also receive a small monetary incentive after participating in each wave of the survey.

The ATP data were weighted in a multi-step process that begins with a base weight incorporating the respondents’ original survey selection probability and the fact that some panelists were subsampled for invitation to the panel. Next, an adjustment was made for the fact that the propensity to join the panel varied across different groups in the sample, as well as to correct for differences between the adults who completed the September and November waves and the adults who did not complete both waves (either because they declined to join the panel, joined the panel but dropped out, or are still active in the panel but did not complete both waves). The final step in the weighting uses an iterative technique that matches gender, age, education, race, Hispanic origin, telephone service, population density and region to parameters from the U.S. Census Bureau’s 2012 American Community Survey. It also adjusts for party affiliation using an average of the three most recent Pew Research Center general public telephone surveys, and for internet use using as a parameter a measure from the 2014 Survey of Political Polarization. Sampling errors and statistical tests of significance take into account the effect of weighting. The Hispanic sample in the ATP is predominantly native-born and English speaking. In addition to sampling error, one should bear in mind that question wording and practical difficulties in conducting surveys can introduce error or bias into the findings of opinion polls.

Of the confirmed members of the panel, 69% responded to both the September and November waves. Taking into account the response rate for the 2014 Survey of Political Polarization (10.6%), the cumulative response rate for the September and November respondents is 3.1%.

Voter file matching

The names and addresses of most panelists were gathered as part of the core American Trends Panel methodology and used to match respondents from the survey sample to their corresponding record in a national voter file. The voter file, gathered by TargetSmart from publicly available individual voter lists from each state, contains information on most voters’ turnout history and selected demographic information (note that the voter file does not indicate for which candidate a person voted, only whether they turned out in that election). To match panelists to the voter file, TargetSmart first looked for exact matches using name, address, and demographic characteristics. A second attempt was made with proximity matching, where a radius is drawn around the given address to test slight variations on the match. In total, 89% of respondents from the September and November waves of the panel were matched to the national voter file.

© Pew Research Center 2016

  1. When data collection for the 2014 Political Polarization and Typology Survey began, non-internet users were subsampled at a rate of 25%, but a decision was made shortly thereafter to invite all non-internet users to join. In total, 83% of non-internet users were invited to join the panel.