“The VP nominee will probably be someone who has been a congressman. Five of the last six republican VP’s were congressmen. Those five were Dick Cheney, Dan Quayle, George H.W. Bush, Gerald Ford, and Richard Nixon. The exception is Sprio Agnew”
Not that you’re suggesting anything more than a useful guide for prediction, but I’d like to point out that there were more pertinent reasons for Cheney and Bush’s nominations than their time in congress. It had a lot more to do with having been the Secretary of Defense, in the case of Cheney, and having come in second place in the primaries (not to mention having been a diplomat and director of the CIA), in the case of Bush. In the case of Ford, of course, those were special circumstances, as congress appointed him instead of the electors voting him in/ Big surprise they’d confirm one of their own.
I agree that many factors were used, to choose the running-mates, including other political experience and balancing the ticket, for geography.