The American Trends Panel (ATP), created by the 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 the September wave of the panel, conducted September 9-October 3, 2014 among 3,154 respondents (2,811 by Web and 343 by mail). The margin of sampling error for the full sample of 3,154 respondents is plus or minus 2.7 percentage points. Among the 1,803 likely voters in the sample, the margin of error is plus or minus 3.5 percentage points.

Data in this report are also drawn from the June wave of the panel and the March Political Polarization and Typology Survey. The June survey was conducted May 30-June 30, 2014 among 3,217 respondents (2,849 by Web and 368 by mail). The margin of sampling error for the full sample of 3,217 respondents is plus or minus 2.3 percentage points.

All current members of the American Trends Panel were originally recruited from the 2014 Political Polarization and Typology Survey, a large (n=10,013) national landline and cellphone random digit dial (RDD) survey conducted January 23rd to March 16th, 2014, in English and Spanish. The margin of sampling error for the full sample of 10,013 respondents is plus or minus 1.1 percentage points.  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.3

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. The final step in the weighting uses an iterative technique that matches gender, age, education, race, Hispanic origin and region to parameters from the U.S. Census Bureau’s 2012 American Community Survey. Population density is weighted to match the 2010 U.S. Decennial Census. Telephone service is weighted to estimates of telephone coverage for 2014 that were projected from the July-December 2013 National Health Interview Survey. It also adjusts for U.S. House Vote Choice among registered voters from the September 2014 national dual frame RDD telephone survey of U.S. adults, 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 American Trends Panel 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.

The Web component of the September wave had a response rate of 60% (2,811 responses among 4,674 Web-based individuals enrolled in the panel); the mail component had a response rate of 61% (343 responses among 560 non-Web individuals enrolled in the panel). Taking account of the response rate for the 2014 Survey of Political Polarization (10.6%), the cumulative response rate for the September ATP wave is 3.5%.

Likely Voter Scale

Likely voter estimates are based on a 7-item turnout scale that includes the following questions: thought (thought given to the election), precinct (ever voted in your precinct or election district), Q.6 (follow government and public affairs), oftvote (how often vote), pgeneral (likelihood of voting), pvote12a (voted in the 2012 presidential election) and scale10 (chances of voting on 1-10 scale). The items are combined to form a seven-point index. The turnout estimate used in identifying likely voters is 40%, which is the approximate average turnout rate over the past few midterm elections. Thus, respondents who score in the top 40% of the distribution are considered to be likely voters. That includes all respondents who received a score of 7 plus a percentage of those who received a score of 6. More details about the Pew Research Center’s methodology for estimating likelihood to vote are available at https://legacy.pewresearch.org/wp-content/uploads/sites/4/2011/01/UnderstandingLikelyVoters.pdf.