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 the panel wave conducted September 16 to September 29, 2019. A total of 6,878 panelists responded out of 7,347 who were sampled, for a response rate of 93.6%. This does not include one panelist who was removed from the data due to an extremely high rate of refusal. The cumulative response rate accounting for nonresponse to the recruitment surveys and attrition is 6.2%. The break-off rate among panelists who logged onto the survey and completed at least one item is 0.8%. The margin of sampling error for the full sample of 6,878 respondents is plus or minus 1.6 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 five strata so demographic groups that are underrepresented in the panel had a higher probability of selection than overrepresented groups:

• Stratum A consists of panelists who are non-internet users. They were sampled at a rate of 100%.
• Stratum B consists of panelists with a high school education or less. They were sampled at a rate of 100%.
• Stratum C consists of panelists that are Hispanic, unregistered to vote, or non-volunteers. They were sampled at a rate of 91.4%.
• Stratum D consists of panelists that are black or 18-34 years old. They were sampled at a rate of 45.1%.
• Stratum E consists of the remaining panelists. They were sampled at a rate of 32.9%.

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

The 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.

Adjusting income and defining income tiers

Family income data reported in this study is adjusted for household size and cost-of-living differences by geography using a similar methodology to Pew Research Center’s previous work on the American middle class. The income tiers used in this analysis are also created following methodology previously used in the Center’s work on the middle class.

Prior to these adjustments, American Trends Panel members were assigned to the midpoint of the income range they selected during the survey to provide an exact income figure for adjustment.

The metropolitan area cost-of-living adjustment is based on price indexes published by the U.S. Bureau of Economic Analysis. These indexes, known as Regional Price Parities (RPP), compare the prices of goods and services across 383 metropolitan statistical areas as well as non-metro areas with the national average prices for the same goods and services. The most recent available data is from 2017.

The national estimates presented in the analysis encompass the U.S. adult population. Those who fall outside of the 371 metropolitan statistical areas found Wave 54 of the ATP are assigned the RPP for their state’s non-metropolitan area.

Family incomes are then adjusted for the number of people in a household using the methodology from Pew Research Center’s previous work on the American middle class. That is done because a four-person household with an income of, say, $50,000 faces a tighter budget constraint than a two-person household with the same income.

“Middle-income” adults live in families with annual incomes that are two-thirds to double the median family income in this ATP sample, after incomes have been adjusted for household size and the local cost of living. The median family income for this sample is about $34,749. Using this median income, the middle-income range is about $40,100 to $120,400 annually for a three-person household. Lower-income families have incomes less than roughly $40,100 and upper-income families have incomes greater than roughly $120,400 (all figures expressed in 2018 dollars).

Two examples of how a given area’s cost-of-living adjustment was calculated are as follows: Jackson, Tennessee, is a relatively inexpensive area, with a price level that is 17.9% less than the national average. The Hawaii metropolitan area known as Urban Honolulu is one of the most expensive areas, with a price level that is 24.4% higher than the national average. Income in the sample is adjusted to make up for this difference. As a result, a family with an income of $45,000 in the Jackson area is equivalent to a family with an income of $68,200 in Urban Honolulu.

© Pew Research Center, 2019