Comparison with Other Data Sources
Estimates of Internet access in the U.S. are on the order of 87%. So despite the fact that the ALP provides Internet access to respondents without prior Internet access (about 10% of the sample), this group is underrepresented. In and of itself, it is not unusual that different groups in the population are differentially represented in the panel. The main question is if one can correct for differential response rates by reweighting. Couper, Kapteyn, Schonlau and Winter (2007) find that conditional on Internet use both the stated willingness to participate in an Internet survey and actual participation are only weakly linked to individual characteristics. This suggests that once weights-based on individual characteristics are applied to ALP data, the resulting sample combining both individuals with and without Internet access will be population representative. This can be further investigated by comparing weighted frequencies in the ALP with external benchmarks.
Weights can be created for each ALP dataset. Figures 1-3 below present comparisons of weighted ALP variables (this is the set of active members of the American Life Panel as of January 2016 who are considered randomly sampled) with weighted Current Population Survey (CPS) variables (CPS March 2015), for males, females, and by number of household members. The weights are calculated using a raking algorithm, as explained in the weighting section. Figure 4 presents a comparison between ALP and CPS with respect to some variables of interest that are both present in CPS and in the ALP, and which have not been used for weighting.
Figure 1: Comparison of weighted frequencies in ALP and CPS, Males
Figure 2: Comparison of weighted frequencies in ALP and CPS, Females
Figure 3: Comparison of weighted frequencies in ALP and CPS, By number of household members
Figure 4: Comparison of weighted frequencies in ALP and CPS, for variables not matched in the weighting algorithm