https://www.mercatus.org/bridge/commentary/value-political-markets
As the election draws nearer, political junkies pay closer attention to poll numbers. But they are well aware of the difficulties and gaps in those numbers. It’s gotten harder to reach truly random samples of voters and harder to be sure they are giving their true opinions since some opinions risk a torrent of graffiti and social ostracism.
Even if a survey generates a valid random sample and gets voters’ honest opinions, a national poll won’t predict results in the Electoral College, which is expected to hinge on six to eight swing states. Those states need to be polled intensively and the results presented for each individually. Finally, once the raw data is collected, pollsters must make educated guesses about which subgroups will actually show up and vote. These assorted guesses and varied polling methods are why so many observers rely on Real Clear Politics polling averages, compiled from several highly regarded sources.
Besides these averages, political analysts now pay close attention to “political betting markets.” The odds in early September show a tight race—making Democrat Joe Biden a favorite to win the presidential race, but only by a few points.