Beware the Bimodal

Missouri incumbent Senator Claire McCaskill thinks Missourians should vote for her because she is in the middle, #50, in a ranking of Senators based on how liberal/conservative they are.

Be careful of the political spin. This ranking doesn’t mean that she’s a ‘centrist’, as she likes to claim. This is the group that does the rankings and here is how it is calculated.

They grade on a curve. Think of a test in high school. If her and fellow Democrat Senators all scored 85 or higher there’s a couple of ways to look at the scores.

First, we might say they all scored well and deserve As and Bs.

Second, we could rank them by their scores and we’d find Claire ranked #50 with a score of 85.

Which method do you think is a better indicator of her true performance? The #50 ranking or the score of 85? I’d argue that the score of 85 is better.

By no means would we say that she’s closer in ability to a person that scores 50 or lower. But that’s exactly what she wants you to believe with her touting of the #50 ranking.

In statistics, a test score distribution where you have a clump of people at 85 and above and another clump of people scoring 40 and below, with very few in between, is a bimodal distribution (or two modes).

In the Senate, you are pretty much either liberal or conservative. Saying you are the least liberal doesn’t mean much, except that you are comfortable misleading people.

While I don’t agree with everything about all conservatives, I don’t very often see a conservative try to mislead folks into believing they aren’t conservative. It should be distressing to liberals when their candidates try to leverage the general public’s weak understanding of statistics to pretend they are not liberal.