I neglected to link last week to a Washington Times op-ed by Gary Andres, a Republican who conducts and analyzes public policy polling projects for the lobbying firm, Dutko Worldwide, that examined the "swing voter universe." His column provided some helpful background on party identification and particularly the follow-up question asked of independents:
[T]here's an important distinction among so-called "independents." Many survey analysts ask a couple of follow-up questions. They ask those who say they are "Republican" or "Democrat" if their partisan affiliation is "strong" or "weak," and they ask independents whether they "lean" toward one party or the other.
These "leaners" are an important group. They represent a large chunk of the independents you read about in polls - in many cases as much as two-thirds of the group. But research has found these Americans are far from "independent." For example, those who "lean Democrat" vote for that party almost as consistently as partisans. The same pattern is true among independents who "lean Republican" - they vote heavily for the GOP. For example, in 2004, according to the American National Election Study poll, 83 percent of independents who "leaned" Democrat voted for John Kerry for president, just shy of his share among Democratic partisans. A similarly high percentage of "lean Republican" independents voted for George W. Bush. Both are a far cry from the conventional view of independents as an unpredictable "swing" group.
Including these "leaners" in the independent camp lumps in a lot of Americans who vote like partisans. That's why some surveys today even group these respondents in the Democratic or Republican camps when reporting partisan results. So, you might read a survey that reports the percentage of Republicans and Democrats "including leaners." That means the pollster has taken a group of people who initially might say they are "independent" and included them in a partisan category. Doing so, at least based on recent voting behavior, makes some sense.
There's more, and late link or not, it's worth reading in full.