statistical calculations from sample site

8 Sample I also employed a more complex statistical process involving three stages: matching followed by a propensity adjustment and finally raking (the techniques are described in detail below). 7 In a previous Pew Research Center study comparing estimates from nine different online opt-in samples and the probability-based American Trends Panel, the sample that displayed the lowest average bias across 20 benchmarks (Sample I) used a number of variables in its weighting procedure that went beyond basic demographics, and it included factors such as frequency of internet use, voter registration, party identification and ideology. Census Bureau, which means that reliable population benchmarks are readily available.īut are they sufficient for reducing selection bias 6 in online opt-in surveys? Two studies that compared weighted and unweighted estimates from online opt-in samples found that in many instances, demographic weighting only minimally reduced bias, and in some cases actually made bias worse. Additionally, they are well measured on large, high-quality government surveys such as the American Community Survey (ACS), conducted by the U.S. These are all variables that are correlated with a broad range of attitudes and behaviors of interest to survey researchers.

Historically, public opinion surveys have relied on the ability to adjust their datasets using a core set of demographics – sex, age, race and ethnicity, educational attainment, and geographic region – to correct any imbalances between the survey sample and the population.

Statistical calculations from sample site