Replies

"The normal.scheme is to poll the R’s and D’s and I’s and determine the best estimate of how each of these 3 groups will split their vote between Obama and Romney. Then they prorate this result based on their independently developed turnout model."

You set your populations however you want. You hopefully true your internals first (as Hewitt hammered home), then sample until the picture emerges (or the money runs out).

Morris did a monster DvR national LV sample in May that I have a lot of respect for:

"From May 5-11, 2012, I conducted a survey of 6,000 likely voters. On such a mammoth sample, the margin of error is less than 1 percent. I found that Romney has amassed a sizable lead over Obama of 51-42, far in excess of what published polling and surveys of registered — as opposed to likely — voters are indicating."