The Astros and Nats both played 20 other teams during the regular season. They didn’t play each other, but they had 12 opponents in common: The had similar records against the 12 common opponents: The Astros won 36 games and lost 24 games for an overall W-L average of .600. The Nats won 35 games and lost 24 games for an overall average of .593.
But … here’s the kicker. Game 6 (and maybe game 7) will be played in Houston. The Astros played at home against 10 of the 12 common opponents. The Nats played on the road against 11 of the 12 common opponents. The Astros’ home record against the 10 teams was 19-12, for a W-L average of .613. The Nats’ road record against the 11 teams was 16-13, for a .552 W-L average. Moreover, the Astros compiled a 50-31 (.617) record at home, while the Nats went 43-38 (.531) on the road.
My numbers are in sync with the betting line. Take the Astros if you’re a betting person. I’m not, but I expect them to win the Series.
But I won’t be at all surprised if the Nats pull off an upset. Single events don’t have probabilities. Non-random events (like physical games) don’t have probabilities. Single, non-random events are unpredictable, which is why people bet on them. If they were predictable, all bets would be off.