There are some demographic differences between undecided voters and those who have made up their minds, but they are small relative to the differences in political interest and engagement. Women are slightly more likely than men to be undecided, younger voters more likely than older ones. There are also small differences across racial groups. Latinos are more likely to be undecided at this point than blacks; whites are in between.

These descriptive differences are negligible compared with differences relating to politics and policy. The YouGov data reveal that undecided voters are much less likely to have positions on issues driving the campaign. On the question of whether the United States should build a wall on its border with Mexico, a position central to Mr. Trump’s campaign for over a year, 28 percent of undecided voters are not sure whether they support or oppose this idea. That’s in contrast to only 7 percent of Mr. Trump’s committed voters (and 11 percent of Mrs. Clinton’s).

Similarly, undecided voters are roughly twice as likely to be unsure whether the minimum wage should be raised or whether college should be free.