KFF Election Tracking Poll: Health Care in the 2018 Midterms

This Kaiser Health Tracking Poll was designed and analyzed by public opinion researchers at the Kaiser Family Foundation (KFF). The survey was conducted September 19th–October 2nd 2018, among a nationally representative random digit dial telephone sample of 1,201 adults ages 18 and older, living in the United States, including Alaska and Hawaii (note: persons without a telephone could not be included in the random selection process). Computer-assisted telephone interviews conducted by landline (301) and cell phone (900, including 605 who had no landline telephone) were carried out in English and Spanish by SSRS of Glen Mills, PA. To efficiently obtain a sample of lower-income and non-White respondents, the sample also included an oversample of prepaid (pay-as-you-go) telephone numbers (25% of the cell phone sample consisted of prepaid numbers) as well as a subsample of respondents who had previously completed Spanish language interviews on the SSRS Omnibus poll (n=10). In addition to the national sample, an oversample was conducted among Florida (599) and Nevada adults 18 and older (599) using both random digit dial technology as well as call backs from the SSRS Omnibus poll of registered voters in each state (including 224 from Florida and 151 from Nevada). Both the random digit dial landline and cell phone samples were provided by Marketing Systems Group (MSG). For the landline sample, respondents were selected by asking for the youngest adult male or female currently at home based on a random rotation. If no one of that gender was available, interviewers asked to speak with the youngest adult of the opposite gender. For the cell phone sample, interviews were conducted with the adult who answered the phone. KFF paid for all costs associated with the survey.

The combined landline and cell phone sample was weighted to balance the sample demographics to match estimates for the national population using data from the Census Bureau’s 2016 American Community Survey (ACS) on sex, age, education, race, Hispanic origin, and region along with data from the 2010 Census on population density. The sample was also weighted to match current patterns of telephone use using data from the July-December 2017 National Health Interview Survey. The weight takes into account the fact that respondents with both a landline and cell phone have a higher probability of selection in the combined sample and also adjusts for the household size for the landline sample, and design modifications, namely, the oversampling of prepaid cell phones and likelihood of non-response for the re-contacted sample. Since the callback sample included registered voters only, the weighted RDD sample was used to estimate the share of registered voters in Florida and Nevada (by party identification). Weighting adjustments for the state samples included specific nonresponse to the callbacks, as well as, in Florida, balancing leaned party identification to the previous 6-month average on the KFF Health Tracking Poll (Nevada and the national sample did not require this adjustment). All statistical tests of significance account for the effect of weighting.

The margin of sampling error including the design effect for the full sample is plus or minus 3 percentage points. Numbers of respondents and margins of sampling error for key subgroups are shown in the table below. For results based on other subgroups, the margin of sampling error may be higher. Sample sizes and margins of sampling error for other subgroups are available by request. Note that sampling error is only one of many potential sources of error in this or any other public opinion poll. Kaiser Family Foundation public opinion and survey research is a charter member of the Transparency Initiative of the American Association for Public Opinion Research.