Update: I wrote this post before Jason Bay's first game with the Sox. Side note: sportswriters still don't get it, noting that Bay had "failed to put the ball in play" in his first five appearances. He had two walks and a hit-by-pitch. He was a baserunner four of the six times he came to the plate. Forget batting average. Ignore batting average. On-base-percentage and slugging percentage. (There are other useful stats, but that's where you should start.)
Prediction is difficult, especially about the future.
When statisticians claim that 80% of the variance in baseball is due to
chance, people leap to the ridiculous conclusion that they mean “baseball is 80% luck.” We all pretty readily conclude that we personally would get a hit off Josh Becket 0% of the time, and would strike out Albert Pujols 0% of the time, so we reject the notion immediately. It is this kind of misunderstanding that leads people to reject statistical analysis in general.
Well, actually, people reject statistical analysis because they don’t want to do any math more complicated than addition and subtraction, but they want a more elevated reason to tell other people.
Variance at the major-league level includes the important detail that you are starting from a pool of people who are the 1000 best in the world at this game. Because they all, even the worst of them, fill up the “skill” portion of the equation to almost 100%, the chance factor looms larger than it would in a pure situation.
Chance is why the better team can lose 11-3 in MLB. The NFL equivalent
score of a better team losing 42-14 never happens. There is chance and
luck in football, of course, but not to nearly the same degree. In baseball, Albert Pujols can hit 3 towering flies to the warning track and go 0-3; a guy you brought up from AAA for a week because of injuries can hit a bleeder through the infield and drive in the winning run. No one looks at that game’s box score and says “OMG, we’ve got to get that guy who outhit Pujols yesterday!”
Two rules of thumb for determining how much a sport’s variance depends on chance are a) how many games they play in a season and b) what percentage of games the championship team loses. These are not independent.
Superior skill in baseball shows over time. Over 162+ games, the slight skill advantage will gradually squeeze out the element of chance.
With that in mind, let’s look at the Ramirez trade. For this season, what is the expected outcome for the Red Sox in wins and losses? (We’ll turn to subsequent seasons in a moment). Sabermetricians usually estimate this in terms of runs. We can’t know in advance whether the runs player A creates will be in a situation that wins games, but we know that over time, creating more runs wins more ballgames. Manny has an Onbase Plus Slugging of .926. Bay has an OPS of .894. Over the remaining 50+ games, that would translate into an estimated 7 extra runs for the Red Sox with Manny in the lineup. That is a difference of 0.4 wins. In a pennant race, that may be significant. It can be the difference between going to the playoffs and going home.
But wait, there’s an extra wrinkle. Manny’s estimated extra runs are predicated on he and Bay having the same number of at-bats. Is that a reasonable assumption? Not at all. They might end up with an equal number of at-bats from here, but Bay has more AB at this point in the season for a good reason: Manny’s been hurt a little. Who is more likely to be hurt and miss games during the rest of the season? Manny, of course, and in Boston, those at-bats would likely be have been picked up by Ellsbury or Crisp. Their OPS for those 10-50 AB must be factored in to Ramirez’s total to get an accurate picture of the trade. The Red Sox have lost about a third of a win this season with this trade, on average. Chance factors make a range estimate more accurate. Boston may lose as many as three wins with the trade; they may gain as many as two wins. Throw in fielding and baserunning, and this is a nearly even trade. For this season.
Next season, they already have a guy under contract who is about 20 runs per season less good than Manny Ramirez, for one-third the price. Those extra millions will go a long way toward paying people you want to get or keep.
The Red Sox robbed the National League blind with this trade.