Gallup has a new report out this morning on how Americans identify themselves when it comes to political party. The results are generating a fair amount of interest, but I’d add a note of caution about the nature of “independents.”

Gallup finds 40% of American self-identify as independents, the highest percentage Gallup has ever measured since it began keeping track. Democrats are a distant second with 31%, with Republicans third at 27%.

What this doesn’t tell us, though, is that the definition of “independent” is far too vague to be of any real value. John Sides had a piece a few years ago that’s worth revisiting.

[H]ere is the problem: Most independents are closet partisans. This has been well-known in political science since at least 1992, with the publication of The Myth of the Independent Voter.

When asked a follow-up question, the vast majority of independents state that they lean toward a political party. They are the “independent leaners.” … The number of pure independents is actually quite small — perhaps 10% or so of the population. And this number has been decreasing, not increasing, since the mid-1970s. […]

The significance of independent leaners is this: they act like partisans…. There is very little difference between independent leaners and weak partisans. Approximately 75% of independent leaners are loyal partisans.

Note that the new Gallup poll shows 40% of Americans self-identify as independents, but when leaners are pressed into one side or the other, the number drops to 10% — exactly where Sides said the number would be when he wrote this more than two years ago.

A variety of pundits will frequently characterize “independents” as a group of “moderate” or “centrist” voters — as if the right sides with Republicans, the left sides with Democrats, and the middle stays “independent.”

That’s a common belief, but it’s also wrong. The Washington Post published a lengthy analysis of political independents in July 2007, based on a survey conducted by the Post in collaboration with the Henry J. Kaiser Family Foundation and Harvard University. The result was a pretty straightforward reminder: there’s an enormous amount of political diversity among independents.

The survey data established five categories of independents: closet partisans on the left and right; ticket-splitters in the middle; those disillusioned with the system but still active politically; ideological straddlers whose positions on issues draw from both left and right; and a final group whose members are mostly disengaged from politics.

The new Gallup numbers shouldn’t change our sense of the current political landscape much at all.

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Steve Benen

Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.