WASHINGTON (CNN) -- The percentage of likely voters who plan to vote for Democrats in Tuesday's congressional elections increased in the past week, and those voters supporting Democrats also seem less likely to change their minds before casting ballots, according to a CNN poll conducted over the weekend.

Democrats hold a 58 percent to 38 percent advantage over Republicans among likely voters in the survey released Monday morning, compared to the 53 percent to 42 percent advantage reflected in the poll a week ago. Pollsters asked people who wires.send-nat-b wires.send-nat-b identified themselves as being likely to vote which party's candidate they would you vote for in their congressional district if the election were being held today.

On this question, the poll has a sampling error of plus or minus 3 percentage points.

In the so-called "poll of polls," which averages the results of five national surveys, the Democrats have a 53 percent to 41 percent margin over the Republicans.

When asked if it is possible they could change their mind before election day, 17 percent of those likely voters who supported Republican congressional candidates said they might instead chose the Democrat, while just 10 percent of those supporting Democrats said a switch was possible.

The poll's sampling error on this question was plus or minus 6 percentage points.

The CNN poll, conducted by telephone on November 3-5 by Opinion Research Corporation, interviewed 1,008 adult Americans, including 636 likely voters.