A recent Gallup poll seems to follow the same pattern. It asked respondents to choose between "Republican," "Democrat," and "Independent" as responses.
I think it's great that "Independents" have reached 45%, but of course there is a glaring problem. "Independents" lumps together moderates that oscillate between the two dominate U.S. parties, "Libertarian Party" members, members of all non-bipolar parties, and the other non affiliated, such as hardcore communists and anarchists. So, on this homepage that gives a few more options.
An additional poll option, including a choice for "single-issue voter/proponent."