When Analysts attack: the predictions don't match their own data

It’s a funny thing about those analysts predicting a “blue wave” of Democratic successes tomorrow: their own race calls don’t match their totals.

Jay Cost of Real Clear Politics fisks them well:

In other words, Rothenberg and Gonzalez are expecting that, though they are convinced that the Democrats are as strong as they have been since Skynyrd’s Second Helping, and though they have presumably completed a thorough search for any GOP seat with even the vaguest sign of weakness, they nevertheless believe that they have systematically underestimated Democratic strength by 30% to 60%!

That is a lot of error to commit when you are on the look-out for exactly that type of error.

Why are they doing this?

My read of Rothenberg, and Cook for that matter, is that they do not want to be on the low side of the next “1994.” They want to minimize the probability of the false negative, i.e. Type II error. In other words, they do not want to fail to predict a seat will switch when it indeed will switch. Or, in the aggregate, they do not want to underestimate Democratic gains.

(Bold emphasis mine). Read the whole thing at the link above. Cost uses statistics to drive his point home, but you can just look at the race-by-race calls from either Cook or Rothenberg to know they can’t be right on both their overall claims for a Democratic “wave” and on the individual races.

Cross-posted at Wizbang! Politics with extended quote.