The analysis in this report is based on a web survey conducted September 30-October 11, 2011 among a sample of 1,168 adults, 18 years of age or older. The survey was conducted by Knowledge Networks (KN) among a random sample of households in their nationally representative online research panel. KN panel members are recruited through probability sampling methods and include both those with internet access and those without. (KN provides internet access for those who do not have it and, if needed, a device to access the internet, when they join the panel.) A combination of random digit dialing (RDD) sampling and address-based sampling (ABS) methodologies have been used to recruit panel members; in 2009 KN switched their sampling methodology from RDD to ABS. The panel includes households with landlines and cell phones, as well as those without a telephone. Both the RDD and ABS samples were provided by Marketing Systems Groups (MSG). KN continually recruits new panel members throughout the year, to offset panel attrition as people leave the panel. The survey was conducted in English. Respondents were selected randomly from eligible adult household members of the panel. All sampled members received an initial email on September 30 to notify them of the survey and included a link to the survey questionnaire. One follow-up reminder was sent to those who had not yet respondent on October 4.
The final sample for this survey was weighted using an iterative technique that matches gender, age, education, race, Hispanic origin, region, and metropolitan area (or not) to parameters from the August 2011 Census Bureau’s Current Population Survey (CPS). In addition, the sample is weighted to match current patterns of internet access from the October 2009 CPS survey. This weight is multiplied by an initial base or sampling weight that corrects for differences in the probability of selection of various segments of KN’s sample and by a panel weight that adjusts for any biases due to nonresponse and noncoverage at the panel recruitment stage (using all of the parameters mentioned above as well as household income and home ownership status). Details about the KN panel-level weights can be found at http://www.knowledgenetworks.com/knpanel/KNPanel-Design-Summary.html.
Sampling errors and statistical tests of significance take into account the effect of weighting at each of these stages. Sampling error for the total sample of 1,168 respondents is plus or minus 3.5 percentage points at the 95% level of confidence. Sample sizes and sampling errors for other subgroups are available upon request.
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.