04/22/2008 05:12 am ET Updated May 25, 2011

Clinton's Pennsylvania Lead: Is It Really 20 Points?

A new survey showing Sen. Hillary Clinton leading Sen. Barack Obama by 20 percentage points in Pennsylvania comes from a polling firm with a shaky track record this election season.

The poll, which topped the Drudge Report on Monday afternoon ("shock poll"), was issued by American Research Group Inc. (ARG). In the poll, conducted on Friday, Saturday and Sunday, 57% of likely Democratic voters said they were supporting Sen. Clinton, compared with 37% for Sen. Obama. Just last week, each candidate received 45% in an ARG poll in the state. Other recent polls generally show a much smaller Clinton lead.

But there are reasons to question ARG polling numbers. In a polling report card of 2008 primary accuracy issued by a rival survey company, ARG ranked in the bottom half of more than three dozen polling firms, among 2008 primaries through late February. It also ranked near the bottom in another ranking of pollster accuracy at fivethirtyeight.com, a Web site that tracks the Electoral College. And, as I wrote last month, the widely tracked polling averages at the political Web site Real Clear Politics don't include ARG numbers, because of concerns about transparency. Like they've been in Pennsylvania, ARG polls also were volatile in previous primaries, notably in Wisconsin, which saw a 16-point swing in just two days.

Keep reading here.

Click here for an extensive list of Pennsylvania polls.