I've been re-reading Baseball Between the Numbers, a collection of intriguing and challenging essays on our favorite game by a group of Baseball Prospectus writers (ed. Jonah Keri). In "Is Alex Rodriguez Overpaid?", Nate Silver discusses the probability of a team making the playoffs based on its number of wins. Looking at the 1996-2005 seasons, Silver found that winning exactly 80 games gave a team only a 0.8% chance to make the playoffs. Exactly 85 wins bumped it to 9.3%, but exactly 90 wins jumped that to 56.5%. Winning exactly 95 games was a sure bet (94.3%), and winning exactly 100 was a near-certainty (99.5%). Mr. Silver calls the range between 86-93 wins "the sweet spot," as a graph of the playoff probabilities shows a sharply-increasing slope in that region. He points out that "winning 90 games rather than 89, for example, improves a team's chances of making the playoffs by about 13 percent."
If winning 90 games gives us a greater than 50-50 shot at reaching the post-season, what are the chances that we will win 90 games? I figure we have about a 1-in-10 probability of winning 90, and if I multiply 0.1 times 0.5 or 0.6, I get only a 5-6% chance of an October opportunity. I do give us a 50% chance of landing in Mr. Silver's "sweet spot," which is encouraging if you think the West will be wide open and no one club will run away with it (which I believe to be the case). If I stretch my limited optimism to 2-in-10 or 20%, that doubles the result to 10-12% which still seems reasonable when I imagine Aubrey Huff and Bengie Molina chugging down the line. If you think we have a 50-50 chance of winning 90 (like JCP) that improves the chances to (0.5 x 0.5 and 0.5 x 0.6) about 25-30%. Again, this is just based on the idea that 90 wins gives you a 50-60% (actually 56.5%) chance of making the playoffs. Winning more than 90, of course, improves your chances dramatically.
Here's your homework assignment: think about the 2010 Giants chances to win 90 games and multiply that by .565 (or just cheat like me and use a range from 0.5 to 0.6). What do you think about those odds?