Basketball R.P.I. vs Sagarin Rating (Question & Answer)

[Turbine]

How do you figure the Strength of Schedule?

It's 2/3 opponents' winning percentage and 1/3 opponents' opponents' winning percentage.

[Turbine]

Why do the rankings seem so weird early in the season?

The RPI is primarily a measurement of strength of schedule and how the team did against that schedule and each season stands on its own. Consequently, the numbers can really skewed early in the season because teams have played so few games. For example, a team can be 2-0, but its opponents haven't played anyone else yet, so its strength of schedule is 0. That's 75% of the formula, so the team won't be rated very highly. The data starts to take shape and look reasonable as conference play gets into full swing around the end of December. And the more games played, the better the data gets.

[Turbine]

Why is my team's record wrong?

The RPI is calculated using games between full-fledged Division I (D-I) opponents only. All 318 full-fledged D-I teams are listed in the rankings. If a school plays a team not listed in the rankings, that game doesn't count and won't be reflected in the records or results.

[Turbine]

Why is my team ranked behind this other team when we beat them?

The RPI is a measurement of strength of schedule and how you did against that schedule. The ENTIRE schedule. To look at only one game ignores the "any given day" aspect of sports. In 1998-99, for example, Iowa lost to Creighton, who lost to Drake, who lost to Evansville, who lost to East Carolina, who lost to James Madison, who lost to Maryland-Eastern Shore, who lost to Delaware St., who lost to New Hampshire, who lost to Yale. No one in their right mind would have rated Iowa behind any of those teams, let alone all of them.

[Turbine]

Why did my team move up after a loss (or down after a win)? Why did my team move up (or down) when they didn't play?

There could be several reasons. One is that since the RPI measures strength of schedule, so it is possible to have a higher RPI after playing a good team, win or lose. Also, a team could have its RPI move down by playing a bad team, win or lose. A team's RPI can also change when they don't even play if one of the teams on their schedule played.

Another thing is that rankings are relative, meaning that a team's ranking is affected by the results of teams around them in the rankings. A team could move in the rankings without even playing if the teams around them played. This is the way computer models can work and is often the most confusing difference for people used to following polls.

[Turbine]

How is the RPI different from the Sagarin ratings?

There are two main differences between the RPI and Sagarin's ratings:

The RPI only cares whether or not a team wins, whereas Sagarin takes into account other things like the margin of victory, game location, etc.

Sagarin's ratings also have a starting point, based on last year and I think Jeff's opinion of how teams should do. I'm certain that starting point is no longer included by the end of the year, however, so that each year can stand on its own. The RPI starts everyone from scratch. That's why it's not terribly informative until around midseason.

Also, Sagarin doesn't really release any information about his formula, since he invented it and sells the results, while the basic formula for the RPI is available to anyone who has a computer and too much time on their hands.