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.
