What polling errors from recent elections can tell us about 2016's closest Senate races
As Election Day approaches, the volume of polling has increased. It’s easy for any individual poll to be wrong for a variety of reasons. However, we can reduce the chance for error from any single poll by combining it with many other polls in a statistical average, which is just what Huffington Post Pollster and Daily Kos Elections do.
These averages are essential for giving us the lay of the land in key races, like those that could determine which party controls the Senate in 2016. Of course, averages are only as accurate as the underlying body of polls they collect, and even these aggregates can miss a race by several points or fail to predict the correct winner. Polling in 2012 systematically underestimated Democrats while 2014 polls did the opposite. Still, some states have polling errors more consistently in favor of one party than other states do.
Below, we’ll take a look at Pollster’s averages over the last four elections compared to the actual results in the four states we currently rate as “Tossups” in the fight for the Senate: Indiana, Nevada, New Hampshire, and Pennsylvania. Although the low number of races for each state unavoidably yields a small sample size that lacks strong predictive power, we can still investigate whether these polling errors might still be able to tell us anything about this year’s Senate battlegrounds.
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