According to nonpartisan and Republican polls, Rep. Paul Kanjorski (D-Pa.) is one of the most endangered incumbents in the country. But public Democratic polls tell an entirely different story.

A recent Oct. 8-12 Franklin & Marshall College survey showed Hazelton Mayor Lou Barletta (R) leading the Congressman 40 percent to 35 percent. That poll came on the heels of an Oct. 6-8 Research 2000 survey for the liberal Daily Kos Web site that showed Barletta with an advantage of 43 percent to 39 percent.

A third poll, conducted Oct. 2 by Susquehanna Polling and Research for Barletta’s campaign, also gave the Republican an edge of 47 percent to 39 percent.

But the Democratic Congressional Campaign Committee released an Oct. 5-6 Grove Insight (D) poll showing Kanjorski ahead comfortably, outside the margin of error, 47 percent to 39 percent.

So what explains the dramatic discrepancy in the surveys? The difference could be in the partisan makeup of the samples.

Self-identified Republicans made up 34 percent of the sample in the Franklin & Marshall poll, 35 percent in the Research 2000 poll and 33 percent in Barletta’s polling. On the other hand, likely Republican voters constituted only 25 percent of the sample in the Grove survey done for the DCCC.

Self-identified Democrats made up 60 percent of the sample in the Franklin & Marshall poll, 48 percent in the Research 2000 poll and 58 percent in the Susquehanna survey, compared with 50 percent in the Grove Insight poll.

Another large difference was in the number of self-described independent or “other” voters tested in the polls. Those voters made up 26 percent of the sample in the DCCC poll, compared with 17 percent in the Research 2000 survey, 6 percent in the Franklin & Marshall survey and 8 percent in Barletta’s polling.

It’s unclear whether the lower Republican or higher independent sample explains Kanjorski’s advantage in the Democratic polling. It could be a combination of both. The lower Republican percentage could be depressing Barletta’s support, and Kanjorski could be getting a bump from the larger number of independent voters, who have been more likely to favor Democrats over the last three years.

The presidential ballot in these surveys complicate things a little further because Sen. Barack Obama (D-Ill.) had a wide 20-point lead in Barletta’s survey and a 15-point advantage in the Grove survey. Research 2000 gave Obama just a 4-point edge, while Franklin & Marshall had his lead at 9 points.