From FiveThirtyEight.com’s Building a Bracket Is Hard This Year, But We’ll Help You Play the Odds:

So how were the Cardinals a No. 4 seed?

The answer, almost certainly, is the selection committee’s attachment to Ratings Percentage Index (RPI), which somehow evaluates Louisville as only the 18th-best team in the country. RPI, as I’ve written previously, was “developed in 1981 in the era of the DOS prompt and the Commodore 64.”