Governors vs. Senators

There is plenty of talk of Governors making better presidential candidates than Senators. Senators are said to lose while Governors win. The usual reason cited is executive experience. I decided to see for myself whether this was the case. I looked at all of the presidential elections since 1900. I divided candidates into four categories.

1) Senators - candidates whose last elected office was Senator (not necessarily a sitting Senator)
2) Governors - candidates whose last elected office was Governor (not necessarily a sitting Governor)
3) Presidents/Vice Presidents - candidates whose last elected office was President or Vice President (not necessarily a sitting President or Vice President)
4) All others (Congressmen, Supreme Court Justices, Businessmen) Senators won the presidency 2 out of 7 times (29%).

Governors won the presidency 6 out of 14 times (43%). Presidents/Vice Presidents won 16 out of 25 (64%). Using the Governors value as a baseline probability, and a cumulative binomial distribution, there is a 36% probability that the Senators would only win 2 contests out of 7 tries. Not a high percentage, but certainly not prohibitive; ergo, Senators are not really disadvantaged compared to Governors. In comparison, there is only a 3% probability that the Pres/Vice Pres would win 16 of 25. This indicates that the Presidents and Vice Presidents definitely have an edge over Governors or Senators. A couple of interesting tidbits. While Governors and Senators are statistically fairly even, Governors have received twice as many nominations as Senators. Only once have we had a Senator vs. Governor matchup, in 1920 and the Senator won.