The collective total of independents grew by about 443,000 in Colorado, Florida, Iowa, Nevada, New Hampshire and North Carolina since the 2008 election, according to data compiled by Bloomberg from state election officials.

During the same time, Democrats saw a net decline of about 480,000 in those six states, while Republicans — boosted in part by a competitive primary earlier this year — added roughly 38,000 voters in them, the analysis shows.

“Democrats hit the high-water mark for registration in 2008, so it’s natural that they are going to see some drop off,” said Michelle Diggles, a senior policy analyst with the Democratic-leaning Third Way research group in Washington who conducted a similar study earlier this year.

The rise of independent voters has had a major impact on recent election results.