That’s because an entrance-exit poll isn’t a random sample of the population like a normal poll. It’s a random sample of precincts, usually between 15 and 60 in a state exit poll. This one had just 25 precincts. Race is not usually used as a criteria for selecting precincts.

Precinct selection introduces a whole new dimension of error into an entrance-exit poll for Hispanic voters, or any demographic group that’s concentrated in small areas. The 25 precincts could overrepresent an unrepresented group — imagine if a New York exit poll, by chance, included two Orthodox Jewish precincts in Brooklyn and showed a Republican ahead among Jewish voters — or completely miss a small, geographically concentrated group.

You can imagine how this could wind up creating the opposite risk of the precinct analysis: What if the entrance-exit poll simply doesn’t include a heavily Hispanic precinct where Mrs. Clinton excelled? The danger is real with a sample as small as this, especially in a highly diverse state.

This type of problem is responsible for one of the biggest exit poll controversies in memory: the finding that 44 percent of Hispanic voters supported George W. Bush in 2004. Simply by chance, 3 of the 11 plurality Hispanic precincts were in Miami-Dade County, where Hispanic voters are particularly conservative. The 44 percent finding was four points higher than the result from a compilation of the 50 state exit polls — a difference well outside the formal “margin of error” for a sample of that size.

The exit pollsters are upfront about the issue, as they acknowledged in the exit poll’s postelection analysis in 2004:

“A National Sample of 250 precincts can do a good job estimating all of the broad characteristics of the electorate, but it is not designed to yield very reliable estimates of the characteristics of small, geographically clustered demographic groups. [...] If we want to improve the National Exit Poll estimate for Hispanic vote (or Asian vote, Jewish vote or Mormon vote etc.) we would either need to drastically increase the number of precincts in the National Sample or oversample the number of Hispanic precincts.”

And that’s for a national exit poll of 10 times as many precincts as the one in Nevada.

The exit polls have also been criticized for other issues measuring Hispanic voters, like whether pollsters conduct Spanish-language interviews. They generally do not, although Spanish-language questionnaires are typically offered in Nevada and other states with large Hispanic populations.

In a December interview, Joe Lenski, who runs the exit polls for Edison Research, acknowledged that exit polls “are not the precise measurement of demographics that people would want them to be.” He said that he “cringes” when people say “Oh, that’s the number” and run with it as “absolute truths or precise numbers.”