April 19, 2021 Welcome to the first week of the FanGraphs Power Rankings. Nearly every major sports site has some form of power rankings; It’s a fun way to think about all 30 teams in baseball and stack them up against each other outside of the rigid structures of leagues and divisions. But where most sites use a panel of experts to build their power rankings — experts who may or may not be simply using their gut feeling to rank teams — I wanted to build an approach to power rankings that was a little more data driven. My approach basically boils down to taking the three most important components of a team — their offense (wRC+), their starting rotation (SP FIP-), and their bullpen (RP FIP-) — and weighting and adjusting to create an overall team quality metric. I played around with trying to include defense in some form, but adding UZR or DRS or defensive efficiency never really made the team quality metric any more accurate. To test my comprehensive team metric, I used 2020 data to see how it correlated with each team’s win percentage at the halfway mark and their final record. The correlation coefficient at the middle of the season was .68 with an r-squared of .47, and at the end of the season, those marks improved to .80 and .63, respectively.