The odds for Democratic Sen. Joe Biden succeeding Barack Obama during his first year if elected? About 5 percent, John Banzhaf, a George Washington University Law School professor, said in a release.

McCain's heavy smoking earlier in life, plus his age -- 72, if he wins -- suggest Palin would have up to a 40 percent chance of taking over for him, Banzhaf said. McCain, a Republican senator from Arizona, has about a 20 percent chance of dying as a former heavy smoker and a greater risk of disability, in addition to the risk he has from the melanoma removed in 2000.

Because of his age, Obama has a less than 5 percent chance of dying within the next 10 years because of smoking, Banzhaf said. Even if the Illinois senator were classified as a current smoker -- Obama said he quit but occasionally lapses -- his 10-year risk is less than 10 percent.

Banzhaf said his estimates were based on 2008 National Cancer Institute tables that include smoking when calculating the odds of dying.