538.com launched an interactive to track Trump’s job approval and disapproval ratings. Although the topline results are fairly similar to other approval-rating averages such as the ones from Real Clear Politics and Huffington Post Pollster — we currently have Trump’s approval rating at 44 percent and his disapproval rating at 50 percent — our version has a few extra features that add a bit of rigor and make it uniquely FiveThirtyEight-ish. Here is the most recent polling: https://projects.fivethirtyeight.com/polls/president-general/national/
As with our election forecasts, we use almost all polls but weight them based on their methodological standards and historical accuracy. We adjust polls for house effects if they consistently show different results from the polling consensus. And we account for uncertainty, estimating the fairly wide range within which Trump’s approval ratings could vary over the next 100 days. (This is what’s indicated by the green and orange bands on the chart.) Here’s a more detailed — and at times, technical — rundown of how we crunch the numbers.
Our philosophy is to use all the polls we can find — provided that we think they’re real, scientific surveys. However, we use a formula that weights polls according to our pollster ratings, which are based on pollsters’ historical accuracy in forecasting elections since 19982 and a pair of easily measurable methodological tests:
Whether the pollster participates in professional initiatives that seek to increase disclosure and enforce industry best practices — the American Association for Public Opinion Research’s transparency initiative, for example. Whether the pollster usually conducts live-caller surveys that call cellphones as well as landlines. Polls are also weighted based on their sample size, although there are diminishing returns to bigger samples. Surveying 2,000 voters substantially reduces error compared with surveying 400 of them, but surveying 10,000 voters will produce only marginal improvements in accuracy compared with the 2,000-person survey. The worse the pollster’s rating, the quicker it encounters diminishing returns in our formula; a Zogby Interactive survey still wouldn’t get much weight in our model, for example, even if it polled 100,000 people.
The weights also account for how often a pollster measures Trump’s approval ratings. If it does so more often than about once per 20 days, each instance of the poll is discounted so that the pollster doesn’t dominate the average just because it’s so prolific. Daily tracking polls also receive special handling from the formula so that interviews are not double-counted.
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