FanGraphs Power Rankings: July 1–7
These next few weeks should go a long way towards separating the wheat from the chaff in the postseason race. For the teams on the fringe of the playoff picture, a timely hot streak could convince them to upgrade at the trade deadline, while a cold snap could push them into seller mode. With the All-Star break looming, it’s time for some serious introspection as teams gear up for the stretch run.
This season, we’ve revamped our power rankings. The old model wasn’t very reactive to the ups and downs of any given team’s performance throughout the season, and by September, it was giving far too much weight to a team’s full body of work without taking into account how the club had changed, improved, or declined since March. That’s why we’ve decided to build our power rankings model using a modified Elo rating system. If you’re familiar with chess rankings or FiveThirtyEight’s defunct sports section, you’ll know that Elo is an elegant solution that measures teams’ relative strength and is very reactive to recent performance.
To avoid overweighting recent results during the season, we weigh each team’s raw Elo rank using our coinflip playoff odds (specifically, we regress the playoff odds by 50% and weigh those against the raw Elo ranking, increasing in weight as the season progresses to a maximum of 25%). As the best and worst teams sort themselves out throughout the season, they’ll filter to the top and bottom of the rankings, while the exercise will remain reactive to hot streaks or cold snaps. Read the rest of this entry »