I don't think that's the definition usually used for "independent" when talking about voter affiliation. US politics has a long history of people telling pollsters (and filling out voter affiliation info in actual elections) that they aren't affiliated with a specific party because political parties have generally historically been seen pretty negatively in the US. In reality, many of these self-identified "independent" voters have voting records that are heavily skewed (if not straight-ticket) to one party or another. I don't have actual numbers on what % of independents this is (I too am interested in the parent's question on this matter), but it's definitely not a "definitionally, none" answer.