WASHINGTON, D.C. -- Rep. Betty McCollum joined ranks with some extremely left-leaning company today as one of a dozen members of the House of Representatives with the most liberal voting record in 2008.

In the annual ranking of votes by the National Journal Magazine, the Minnesota delegation split up as follows:

But, what does this really tell us? According to Steve Smith, political science professor at Washington University, not as much as some people may think.

National Journal’s vote ratings are determined by analyzing “key” votes, which are then separated into three categories: economic, social and foreign policy.

“There is a substantial subjectivity in the choice of votes,” said Smith. “So there is an awful lot of variation year-to-year.”

Last year, for instance, McCollum ranked as the 46th most liberal member in the House.

More importantly, Smith said, the parties are so polarized that while these changes in ranking may seem large, they often represent only a handful of votes. Therefore, even the most liberally ranked Democrat, like McCollum, is not that much different than, say, Rep. Tim Walz, D-Minn., who ranked 175th on the liberal voting scale for last year, according to Smith.

“We have highly polarized parties, so the distinctions among Democrats and Republicans are really matters of small degrees,” Smith said.

(Check out these cool graphs [PDF] that Smith whipped up with the new data to prove his point.)

So, given all that, what’s the take-away?

At the very least, the data allows political scientists like Smith to graph out voting patterns in order to understand how Congressional lawmakers fall along the ideological spectrum. And, of course, how that pattern has changed over time.

“There are lots of ways of rating, or looking, at how members of Congress act and vote,” said National Journal Congressional reporter Richard E. Cohen.

“The value of ours, from our perspective, is that we rate members on an ideological spectrum,” Cohen said. “We rate them relative to each other on the votes that we select. We are not setting up what is liberal or what is conservative. The members are by how they vote.”

Smith’s point, then, is that in about the last two decades Congressional Democrats and Republicans have largely voted very consistently, and thus predictably, along party lines.

“For a voter that is completely in the dark, I suppose these scales tell you something,” said Smith. “But, over the last roughly 20 years... just knowing somebody’s party label tells you about as much.”