PRINCETON, NJ -- The Democratic candidates lead Republican John McCain among unmarried voters, while McCain bests both Barack Obama and Hillary Clinton among married voters.

These results, based on interviews with more than 18,000 registered voters from Gallup Poll Daily tracking in May, are similar to what Gallup has observed in recent presidential elections.

In the last three presidential elections, the Republican candidate has fared better among married voters of either gender -- winning all of the marriage-by-gender groups except married women in 1996, which Bob Dole lost narrowly to Bill Clinton. Meanwhile, the Democratic candidate has won among unmarried voters of both genders in all three elections since 1996. (Gallup does not have data for the vote by marital status prior to the 1996 election.)

Usually, of the four marriage-by-gender groups, married men show the greatest support for the Republican candidate and unmarried women most strongly back the Democratic candidate. The degree to which those relationships hold in 2008 depends in part on which candidate the Democrats eventually nominate.

If, as seems likely, Obama is the Democratic nominee, he would enter the general-election phase of the campaign with commanding leads among both unmarried men and unmarried women. He leads McCain by 23 percentage points among unmarried women and by 16 points among unmarried men.

In turn, McCain outpolls Obama by a wide 17-point margin among married men, but holds a smaller 6-point advantage among married women.

The picture would look somewhat different if Clinton were the Democratic nominee. She would, like Obama, lead McCain among both unmarried groups, but by a larger margin among unmarried women (31 points) and by a smaller margin among unmarried men (6 points). McCain would fare just as well among married men vs. Clinton as he does against Obama, but these data suggest Clinton and McCain would be highly competitive for the votes of married women.

No doubt these relationships reflect Clinton's appeal to female voters, who have been among her most reliable supporters in the Democratic primaries. It is unclear whether Obama would be able to increase his standing among female voters if he were the Democratic nominee. But any disadvantage he has among female voters he has tended to make up for with greater support among blacks and young people.

Implications

These results suggest that the marriage gap evident in the past few elections will likely persist in 2008 as well, with McCain typically leading among married voters and the Democratic candidate leading among unmarried voters. Of the four marriage-by-gender groups, married women seem to be the most competitive, with Clinton and McCain essentially running even and McCain holding only a modest lead versus Obama among this group.

Survey Methods

Results are based on telephone interviews with 18,462 registered voters nationwide, aged 18 and older, conducted May 1-21, 2008, as part of Gallup's daily tracking survey. For results based on the total sample of national adults, one can say with 95% confidence that the maximum margin of sampling error is ±1 percentage point.

For results based on the sample of 6,085 registered voters who are married men, the maximum margin of sampling error is ±1 percentage point.

For results based on the sample of 2,965 registered voters who are unmarried men, the maximum margin of sampling error is ±2 percentage points.

For results based on the sample of 4,539 registered voters who are married women, the maximum margin of sampling error is ±2 percentage points.

For results based on the sample of 4,762 registered voters who are unmarried women, the maximum margin of sampling error is ±2 percentage points.

Interviews are conducted with respondents on land-line telephones (for respondents with a land-line telephone) and cellular phones (for respondents who are cell-phone only).

In addition to sampling error, question wording and practical difficulties in conducting surveys can introduce error or bias into the findings of public opinion polls.

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