PRINCETON, NJ -- The latest Gallup Poll Daily tracking report from Monday through Wednesday shows Barack Obama with a 49%to 43% lead over John McCain among registered voters.

Almost all of the interviews in this three-day rolling average were conducted before Wednesday night's third and final presidential debate at Hofstra University, which began at 9 p.m. ET. It will be several days before the full impact of this debate can be measured in the three-day rolling average, although its initial impact might be apparent as early as Friday's report.

Meanwhile, the current rolling average shows that McCain has done slightly better in the days leading into the debate. McCain's 43% share of the vote matches his best in the last two weeks. Today's average also represents the first time since the Sept. 30 - Oct. 2 average that Obama has received less than 50% support from registered voters, although Obama continues to maintain a significant lead among this group. (To view the complete trend since March 7, 2008, click here.)

Gallup is presenting two likely voter estimates to see how preferences might vary under different turnout scenarios. The "expanded" model determines likely voters based only on current voting intentions. This estimate would take into account higher turnout among groups of voters traditionally less likely to vote, such as young adults and minorities. That model has generally produced results that closely match the registered voter figures, but with a lower undecided percentage, and show Obama up by six percentage points today, 51% to 45%.

The "traditional" likely voter model, which Gallup has employed for past elections, factors in prior voting behavior as well as current voting intention. This has generally shown a closer contest, reflecting the fact that Republicans have typically been more likely to vote than Democrats in previous elections. Today's results show Obama with a two-point advantage over McCain using this likely voter model, 49% to 47%, this is within the poll's margin of error. -- Frank Newport

(Click here to see how the race currently breaks down by demographic subgroup.)

Survey Methods

For the Gallup Poll Daily tracking survey, Gallup is interviewing no fewer than 1,000 U.S. adults nationwide each day during 2008.

The general-election results are based on combined data from Oct. 13-15, 2008. For results based on this sample of 2,786 registered voters, the maximum margin of sampling error is ±2 percentage points.

For results based on the sample of 2,143 "traditional" likely voters (based on the model taking into account current voting intention and past voting behavior), the maximum margin of sampling error is ±2 percentage points.

For results based on the sample of 2,312 more broadly defined likely voters (based on the model taking into account current voting intention only), the maximum margin of sampling error is ±2 percentage points.

Interviews are conducted with respondents on landline telephones (for respondents with a landline 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.