Thursday, May 24, 2012

Your Lyin' Eyes: Why the NBC Marist Poll is Not Good News for the President

Once again, a prestigious polling organization publishes a presidential election poll with provocative top-line numbers, but once again, it's the poll's internal numbers that provide the real news. On Tuesday, it was the Quinnipiac poll showing Mitt Romney with a 6 point lead in Florida that was misleading because it underpolled Democrats. Today, it's the NBC News Marist poll of battleground states showing Obama with a lead. Why are those results suspect? Let's take a look.

In Ohio, according to the poll, Obama has a 48%-42% lead over Romney and NBC reports a
D=37  R=28  I=34 voter identification breakdown.

The problem is that the actual Ohio breakdown is
D=36  R=37  I=27.

Republicans were underpolled by 9%. There's Obama's margin in the poll.

The same is true for Florida. The poll results show Obama leading Romney 48%-44%, with a party breakdown of:
D=43 R=35 I=21

The actual party breakdown in Florida is:
D=36 R=40 I=24

Again, NBC News oversampled Democrats by 7% and undersampled Republicans by 5%. That's why Obama is leading. And even with that much discrepancy, he's only leading by 4%. Not good.

Virginia likewise provides little reassuring news for the president. The poll's party breakdown was:
D=39 R=29 I=39

And the actual  party registration in Virginia is:
D=36 R=39 I=25

Again, Republicans were undersampled to the tune of 10%. So with a 48%-44% lead, that undersampling is Obama's margin.

All three of these states are close and will remain so throughout the campaign. It would be nice if the pollsters were giving us more accurate information.

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