WASHINGTON -- Another new poll in Massachusetts -- the sixth to be released since the end of the Democratic convention -- but unlike the other five, this one shows Republican Sen. Scott Brown holding a narrow lead over Democratic challenger Elizabeth Warren.

The new poll by UMass Lowell and the Boston Herald found Brown leading Warren by four percentage points (49 percent to 45 percent) among 497 registered voters deemed likely to vote in the November election. The survey was conducted Sept. 13 through Sept. 17, beginning a week after the Democratic convention. The UMass Lowell survey called random samples of both landline and mobile phone numbers.

The five other polls have shown Warren leading by margins varying from two to six percentage points. Relatively small sample sizes likely contribute to the variation. All but one of the new surveys sampled from 400 to 600 likely voters, for reported margins of error ranging from +/- 4 percent to +/- 5 percent.

When combined in the HuffPost Pollster Trend chart, designed to smooth out the random variation inherent in most polls, the new surveys show a virtual dead heat, with Warren just a half percentage point ahead of Brown (46.2 percent to 45.7 percent).

Also on HuffPost:

Loading Slideshow...
  • Virginia

    <strong>For more presidential and congressional polls, maps and forecasts, <a href="http://elections.huffingtonpost.com/2012/romney-vs-obama-electoral-map?hw" target="_hplink">visit HuffPost Pollster</a>.</strong>

  • Missouri

    <strong>For more presidential and congressional polls, maps and forecasts, <a href="http://elections.huffingtonpost.com/2012/romney-vs-obama-electoral-map?hw" target="_hplink">visit HuffPost Pollster</a>.</strong>

  • Massachusetts

    <strong>For more presidential and congressional polls, maps and forecasts, <a href="http://elections.huffingtonpost.com/2012/romney-vs-obama-electoral-map?hw" target="_hplink">visit HuffPost Pollster</a>.</strong>

  • Ohio

    <strong>For more presidential and congressional polls, maps and forecasts, <a href="http://elections.huffingtonpost.com/2012/romney-vs-obama-electoral-map?hw" target="_hplink">visit HuffPost Pollster</a>.</strong>

  • Nevada

    <strong>For more presidential and congressional polls, maps and forecasts, <a href="http://elections.huffingtonpost.com/2012/romney-vs-obama-electoral-map?hw" target="_hplink">visit HuffPost Pollster</a>.</strong>

  • Montana

    <strong>For more presidential and congressional polls, maps and forecasts, <a href="http://elections.huffingtonpost.com/2012/romney-vs-obama-electoral-map?hw" target="_hplink">visit HuffPost Pollster</a>.</strong>

  • Florida

    <strong>For more presidential and congressional polls, maps and forecasts, <a href="http://elections.huffingtonpost.com/2012/romney-vs-obama-electoral-map?hw" target="_hplink">visit HuffPost Pollster</a>.</strong>

  • Michigan

    <strong>For more presidential and congressional polls, maps and forecasts, <a href="http://elections.huffingtonpost.com/2012/romney-vs-obama-electoral-map?hw" target="_hplink">visit HuffPost Pollster</a>.</strong>

  • Wisconsin

    <strong>For more presidential and congressional polls, maps and forecasts, <a href="http://elections.huffingtonpost.com/2012/romney-vs-obama-electoral-map?hw" target="_hplink">visit HuffPost Pollster</a>.</strong>

  • New Jersey

    <strong>For more presidential and congressional polls, maps and forecasts, <a href="http://elections.huffingtonpost.com/2012/romney-vs-obama-electoral-map?hw" target="_hplink">visit HuffPost Pollster</a>.</strong>

  • Pennsylvania

    <strong>For more presidential and congressional polls, maps and forecasts, <a href="http://elections.huffingtonpost.com/2012/romney-vs-obama-electoral-map?hw" target="_hplink">visit HuffPost Pollster</a>.</strong>

  • Arizona

    <strong>For more presidential and congressional polls, maps and forecasts, <a href="http://elections.huffingtonpost.com/2012/romney-vs-obama-electoral-map?hw" target="_hplink">visit HuffPost Pollster</a>.</strong>

  • New Mexico

    <strong>For more presidential and congressional polls, maps and forecasts, <a href="http://elections.huffingtonpost.com/2012/romney-vs-obama-electoral-map?hw" target="_hplink">visit HuffPost Pollster</a>.</strong>