How do we know a president’s approval rating? From polls. But how the poll data are processed makes a difference in what the results are. That becomes clear when we look at the graph above, prepared by Alexander Agadjanian, which shows Trump’s 2017 support this year according to two different kinds of polls:Adjusted for party. The red dots come from YouGov, a survey organization that adjusts its estimates for party identification. That means it estimates approval among Republicans, independents and Democrats, and then averages that over the proportion of these groups in the population. In doing so, it adjusts for any problems that result when a disproportionate number of Democrats or Republicans respond to a particular survey.Not adjusted for party. The black dots come from various other pollsters who did not adjust their polls for party ID.
As you can see, the general time trend is the same for both groups, but the YouGov results are much more stable.Read more at WashingtonPost