October 17, 2019

Modest Changes in Views of Impeachment Proceedings Since Early September

Methodology

The American Trends Panel survey methodology

The American Trends Panel (ATP), created by Pew Research Center, is a nationally representative panel of randomly selected U.S. adults. Panelists participate via self-administered web surveys. Panelists who do not have internet access at home are provided with a tablet and wireless internet connection. The panel is being managed by Ipsos.

Data in this report are drawn from respondents to panel waves conducted September 3 to September 15, 2019 and October 1 to October 13, 2019. Out of 3,954 panelists who were sampled, a total of 3,487 panelists responded to both waves, for a combined response rate of 88%. This does not American Trends Panel recruitment surveysinclude three panelists who were removed from the data due to extremely high rates of refusal of straightlining. The cumulative response rate accounting for nonresponse to the recruitment surveys and attrition is 5.9% for the September wave and 4.9% for the October wave. The break-off rate among panelists who logged onto the survey and completed at least one item is 0.8% for the September wave and 0.9% for the October wave. The margin of sampling error for the full sample of 3,487 respondents is plus or minus 2.2 percentage points.

The sample consisted of all existing panelists who had completed the annual profile survey as of September 9, 2019. Panelists who had not yet completed the profile survey were ineligible. A subsample from the ATP was selected by grouping panelists into six strata so demographic groups that are underrepresented in the panel had a higher probability of selection than overrepresented groups:

The ATP was created in 2014, with the first cohort of panelists invited to join the panel at the end of a large, national, landline and cellphone random-digit-dial survey that was conducted in both English and Spanish. Two additional recruitments were conducted using the same method in 2015 and 2017, respectively. Across these three surveys, a total of 19,718 adults were invited to join the ATP, of which 9,942 agreed to participate.

In August 2018, the ATP switched from telephone to address-based recruitment. Invitations were sent to a random, address-based sample (ABS) of households selected from the U.S. Postal Service’s Delivery Sequence File. In each household, the adult with the next birthday was asked to go online to complete a survey, at the end of which they were invited to join the panel. For a random half-sample of invitations, households without internet access were instructed to return a postcard. These households were contacted by telephone and sent a tablet if they agreed to participate. A total of 9,396 were invited to join the panel, and 8,778 agreed to join the panel and completed an initial profile survey. Of the 18,720 individuals who have ever joined the ATP, 10,588 remained active panelists and continued to receive survey invitations at the time this survey was conducted.

The U.S. Postal Service’s Delivery Sequence File has been estimated to cover as much as 98% of the population, although some studies suggest that the coverage could be in the low 90% range.1

Weighting

Weighting dimensionsThe ATP data were weighted in a multistep process that begins with a base weight incorporating the respondents’ original survey selection probability and the fact that in 2014 and 2017 some respondents were subsampled for invitation to the panel. The next step in the weighting uses an iterative technique that aligns the sample to population benchmarks on the dimensions listed in the accompanying table.

Sampling errors and test of statistical-significance take into account the effect of weighting. Interviews are conducted in both English and Spanish, but the American Trends Panel’s Hispanic sample is predominantly U.S. 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 following table shows the unweighted sample sizes and the error attributable to sampling that would be expected at the 95% level of confidence for different groups in the survey:

 

Sample sizes and sampling errors for other subgroups are available upon request.

UPDATE: (Oct. 24, 2019): An earlier version of the margin of error table did not include a column for weighted partisan composition.

CORRECTION: (Oct. 22, 2019): An earlier version of the table “American Trends Panel recruitment surveys” reported slightly different totals for the number of active panelists remaining. The table has been updated to reflect the most current numbers. The update does not impact findings.

  1. AAPOR Task Force on Address-based Sampling. 2016. “AAPOR Report: Address-based Sampling.”