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Only registered Democrats vote in Democratic primaries to select Democrat candidates. Only registered Republicans vote in Republican primaries to select Republican candidates. And so forth for other parties.

In general elections most voters registered with a particular party continue to vote for that party. But some defect to another party.

In general elections, what percent of registered party voters defect, on average?

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    Only registered Democrats vote in Democratic primaries this is not true in all states. Some states allow voters not affiliated with a party to vote in any party's primary. – yoozer8 Jan 11 '17 at 14:30
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    Do you literally mean "defect", or simply "vote for different party"? Plenty of people who live in "X-only" politically lopsided states with closed primaries register for party "X" just so they can vote in the primary - since in their state, primary winner for party X is 100% guaranteed to be the winner of general election. But, they still vote for party "NOT X" in general election, because that is their true preference. Semantically speaking, such voters don't "defect", since they weren't truly on party X's side despite being registered. – user4012 Jan 11 '17 at 15:00
  • @user4012, I'd meant "provisionally or temporarily defect", and hadn't considered the plight of, say, a Texan Democrat. Perhaps two-party states, (states with a fluctuating balance of power), should be considered separately from de facto one-party states then. The present question however, (pending further more specific questions), might as well remain about an unparticular sweeping generalization. – agc Jan 12 '17 at 15:23
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14% - 2012 House Elections

The best source of information on US voting behavior is definitely the American National Election Survey. A single slice of their data easily captures hundreds of variables. They utilize a weighted sampling design and panel studies to comprehensively cover the public. What I'm saying is - it's a good study.

The 2016 data isn't available yet, so I downloaded the 2012 data. To answer the question, I focused on the 2012 House of Representatives elections. Variables for other races are available. I excluded people who either were not registered with a party*, or did not vote in this race.

In that election, 86% of Democrats and Republicans voted for the candidate from their own party. The remaining 14% voted for other parties. These percentages were similar for both Democrats and Republicans. In both cases, about 1% voted for independent candidates.


It's worth noting that only 31 states ask voters to register as a member of a party. As such, the data is limited to those 31 states. Because of this difficulty, I did not calculate variance or error values for the percentages above.

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