One of the most bizarre but oft-repeated myths about polling is the
notion that state polls 'lag' behind national polls, and particularly
lag behind national trackers. This is largely a relic of a bygone era
in which newspapers might commission a poll in their state, and then
sit on it for several days until their Sunday editions or some other
ebb in the news cycle. Thus, you might be seeing state polls that were
in the field a week or so ago, whereas the national trackers were more
up-to-date.
This largely is not true today, however.
Rasmussen and SurveyUSA, perhaps the two most prolific public
pollsters, generally release their data no later than 24 hours after it
has left the field; likewise with other pollsters like InsiderAdvantage
and Public Policy Polling. A couple of other pollsters like Quinnipiac
and Mason-Dixon will occasionally sit on a poll for 24-48 hours, but
generally not more than that. Every now and then, you'll have some
small college or some fledgling marketing firm release a poll that is a
couple of weeks old, but this is unusual, and it's easy to notate the
exceptions. Most of the big, business-savvy pollsters recognize the
importance of timeliness in this era of 24/7 news cycles.
Conversely,
some of the national tracking polls are actually not all that fresh.
IBD/TIPP has a 5-day polling window. Battleground also has a 5-day
polling window, and they don't poll weekends, meaning that they're
usually including some data that is a full week old.
Certainly,
there is some mystery as to why the state polls and the national
trackers seem to have diverged somewhat of late, with John McCain
picking up perhaps 2 points in the tracking polls versus last week's
averages, whereas the state polls haven't really budged one iota. The
'lag' effect, however, is not a valid explanation.
--Nate Silver