Who’s right? Who’s wrong? I don’t know. But The Washington Post’s Jennifer Agiesta makes a good point about the dueling polls out today on the potential Specter/Toomey matchup in 2010. (The Franklin & Marshall College Poll has Specter beating Toomey 33%-18%, but Quinnipiac University has Toomey up 41%-27%). The big difference between the two polls is in the wording of the question.

Quinnipiac’s poll asks voters, “If the 2010 Republican primary for United States senator were being held today and the candidates were Arlen Specter and Pat Toomey, for whom would you vote?”

Franklin and Marshall’s question starts off about the same, but watch the big finish, “If the 2010 Republican primary election for U.S. senator were being held today and the candidates included Arlen Specter, Pat Toomey, and Peg Luksik, would you vote for Arlen Specter, Pat Toomey, Peg Luksik, some other candidate, or aren’t you sure how you would vote?”

That final phrase makes all the difference. Quinnipiac’s poll offers voters what we in polling call a forced choice, mimicking the one they would face in the voting booth (unlike Nevada, Pennsylvania does not allow voters to cast a ballot for “none of these candidates”), and as such is a great measure for predicting voter behavior. Franklin and Marshall’s question makes it easier for voters to say they haven’t made up their minds, a perfectly valid response more than a year before anyone has to cast a ballot.