This straightforward story can get lost in the headlines, which tend to give the most attention to the most surprising results — whether it’s a predicted Clinton landslide or a narrow lead for Mr. Trump in key states.

The truth is probably somewhere between those extremes. Pollsters aren’t joking about the “margin of error”: the inevitable random variance in polls that exists simply by chance. If Mrs. Clinton leads by 4 points, you should expect polls that show her with a big lead or locked in a tight race, with others clustered around the average. That’s more or less what we saw this past week.

It’s a lot like baseball. Even great baseball players go 0 for 4 in a game — or have rough stretches for weeks on end. On the other end might be a few multihit nights with extra-base hits, or a spectacular few weeks.

Sometimes, these rough stretches or hot streaks really do indicate changes in the underlying ability of a player. More often, they are just part of the noise inevitable with small samples. Taking more polls is like watching more at-bats, and you need many if you want to be confident about whether a candidate is ahead or tied.