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Politics & Global Warming, Fall 2015


Appendix II: Survey Method

Method

The data in this report are based on a nationally representative survey of 1,330 American adults, aged 18 and older, conducted September 30–October 19, 2015. All questionnaires were self-administered by respondents in a web-based environment. The survey took, on average, about 24 minutes to complete.

The sample was drawn from GfK’s KnowledgePanel®, an online panel of members drawn using probability sampling methods. Prospective members are recruited using a combination of random digit dial and address-based sampling techniques that cover virtually all (non-institutional) resident phone numbers and addresses in the United States. Those contacted who would choose to join the panel but do not have access to the Internet are loaned computers and given Internet access so they may participate.

The sample therefore includes a representative cross-section of American adults – irrespective of whether they have Internet access, use only a cell phone, etc. Key demographic variables were weighted, post survey, to match US Census Bureau norms.

The survey instrument was designed by Anthony Leiserowitz, Geoff Feinberg, and Seth Rosenthal of Yale University, and Edward Maibach and Connie Roser-Renouf of George Mason University.

Margins of error

All samples are subject to some degree of sampling error—that is, statistical results obtained from a sample can be expected to differ somewhat from results that would be obtained if every member of the target population was interviewed. Average margins of error, at the 95% confidence level, are as follows:

Subgroup margins of error are:

  • Democrats (total): Plus or minus 5 points.
  • Liberal Democrats: Plus or minus 6 points.
  • Moderate/conservative Democrats: Plus or minus 7 points.
  • Independents: Plus or minus 9 points.
  • Republicans (total): Plus or minus 5 points.
  • Liberal/moderate Republicans: Plus or minus 8 points.
  • Conservative Republicans: Plus or minus 6 points.

Rounding error

For tabulation purposes, percentage points are rounded off to the nearest whole number. As a result, percentages in a given chart may total slightly higher or lower than 100%. Summed response categories (e.g., “strongly trust” + “somewhat trust”) are also rounded.