RV/LV Gaps & the Myth of a “Wave”

As most people familiar with the literature of the subject will agree, one actual reason for abiding faith in a last-minute Republican “wave” this year is that early polls tend to be of registered voters while late polls focus on likely voters, which is a more Republican universe, particularly in a midterm with a Democrat in the White House. So the RV to LV “switchover” should produce a GOP “surge,” right?

Yes, in theory, but (1) some pollster use LV screens all along, (2) some forecasts bake a switchover factor right into the cake, and (3) the RV/LV gap is by no means uniform.

As an example, check out this notation from Nate Silver yesterday towards the end of a long post reporting some good polling news for Republicans:

A mild piece of good news for the Democrats is that the turnout gap may not be as large as it was in 2010. Both YouGov and NBC/Marist released results among both registered voters and likely voters in each of the states they polled — and on average, their likely-voter models showed the Republican candidate doing a net of about 2.5 percentage points better than in the registered-voter version of their surveys. That’s in line with the historical average gap between registered and likely voters in midterm years — rather than the 6-point gap that persisted throughout 2010.

So again, all the comparisons you’re seeing of the 2010 “wave” may well exaggerate the relevance of that very strange year.

Ed Kilgore

Ed Kilgore, a Monthly contributing editor, is a columnist for the Daily Intelligencer, New York magazine’s politics blog, and the managing editor for the Democratic Strategist.