NEP Revises Texas Hispanic Estimates

Exit Polls Legacy blog posts

I am a bit behind on this item, but the Associated Press issued a "correction" on Monday based on a revision of the exit poll estimate of President Bush’s support among Hispanics in Texas. The correction reduces Bush’s support among Hispanics by ten percentage points (down from the original estimate of 59% to 49%):

The Associated Press overstated President Bush’s support among Texas Hispanics. Under a post-election adjustment by exit poll providers Edison Media Research and Mitofsky International, 49 percent of Hispanics in the state voted for Bush, not a majority. The revised result does not differ to a statistically significant degree from Bush’s 43 percent support among Texas Hispanics in a 2000 exit poll.

The revised BC-TX-Exit-Poll Excerpts showed that 20 percent, not 23 percent, of all Texas voters were Hispanic. They voted 50 percent for Kerry and 49 percent for Bush, not 41-59 Kerry-Bush.

I notice that the Texas exit poll results on CNN.com now reflect this correction. At 49%, Bush’s support among Texas Latino voters was still 6 9 percentage points higher than in 2000 (when it was 43%), but his gains are less than the original exit poll suggested.

Several weeks ago, a source with access to NEP numbers passed along a rumor that NEP would soon revise the national estimate of Bush’s support downwards. On Monday I had also noticed that a recent Washington Post article put Bush’s Hispanic support at 42% rather than the 44% cited both elswhere in the Post and on CNN.com (still 44% as of this writing). Blogger Steve Sailor estimates that the Texas correction alone should reduce Bush’s share of the Hispanic vote to 39% (hat tip: Ruy). So perhaps a national correction is coming as well.

You can get more background on this issue from a recent piece by the Washington Post‘s Fears and from bloggers Ruy Teixeira and Steve Soto. I cannot say much about how or why NEP made this correction, though I will certainly pass along any information that comes my way. If anyone at NEP is reading, I am sure my readers would appreciate an explanation of how you arrived at this revision.

One thing I can explain is the special challenge exit polls face when it comes to small subgroups like Latinos and Jewish voters. The reason is the whole issue of "cluster sampling." Exit polls must sample voters in clusters:  They randomly sample precincts first, then voters at precincts. In a cluster sample, characteristics or opinions that tend to "cluster" geographically tend to have higher rates of sampling error.

The reason is not all that mysterious. Consider the example of Jewish voters in Ohio (a demographic that once included the Mystery Pollster and still includes all of his family, so he speaks from some experience). Most Jews in Ohio live in a few suburbs east of Cleveland and few neighborhoods near Columbus and Cincinnati that cumulatively represent (at most) 3-5% of the state. If the Ohio exit poll sampled only 100 precincts, then most of the Jewish subsample would have come from, at most, 3-5 precincts. Now throw in a kicker: Orthodox Jews tend to be more politically conservative and tend to live among other Orthodox Jews in even more concentrated geographic areas within the Jewish Community. Thus, the odds are good that the exit poll sample will either over or underestimate the share of Orthodox Jews depending which 3-5 precincts get randomly selected. The same problems occurs with Cuban and non-Cuban Latinos in Florida.

So the bottom-line: The potential for error is much greater for a highly clustered demographic group. The fewer clusters in the sample relative, the greater the chance for this sort of error.

Mark Blumenthal

Mark Blumenthal is political pollster with deep and varied experience across survey research, campaigns, and media. The original "Mystery Pollster" and co-creator of Pollster.com, he explains complex concepts to a multitude of audiences and how data informs politics and decision-making. A researcher and consultant who crafts effective questions and identifies innovative solutions to deliver results. An award winning political journalist who brings insights and crafts compelling narratives from chaotic data.