How party ID became partisan — and why it shouldn’t be

After the release of any — and every — swing state or national poll these days, the Fix Twitter feed and email inbox immediately fill up with messages that are some variation on this: “Party ID skewed! D+8!”

That’s political shorthand for a belief that the party identification in the poll — the composition of the sample of people who are being polled — is misaligned to the actual partisan composition of either a state or the country and, therefore, is producing results that are not reflective of the actual state of the race.

The problem with that argument? It’s based on limited information and a series of false assumptions none bigger than that because the country has been virtually evenly divided on partisan lines for the past decade or so that the party identification question should result in something close to a 50-50 split between Democrats and Republicans. That’s not right. [cont.]

Chris Cillizza, Washington Post