In his groundbreaking book “Basketball on Paper”, Dean Oliver hypothesized that there were four elements to basketball success, shooting, turnovers, rebounding, and free throws. He referred to them as the “Four Factors”, a name which has been pretty much universally accepted by the APBRmetrics community. These factors can be thought of as applying both offensive and defensively, so it is reasonable to think of them as eight measures of a teams performance. Much of APBRmetrics theory and analysis consists of developing formulas for measuring both team and individual performance across these four factors.
Most of the reporting and analysis that I do on this site is based on Oliver’s original formulas for studying the four factors. Here’s a rundown of the basics of each.
The most important measure of all is how well does a team shoot the ball. Getting the ball in the basket remains the objective of the game and how well you do that does a long way toward determining whether you are going to win or not. Appropriately, preventing your opponent from scoring is the most important defensive measure.
The generally accepted measure of a team’s shooting ability is effective field goal percentage, or eFG% for short, which combines 2pt and 3pt shots by weighting a made three point shot with an extra 50%. The specific formula is:
The second most important factor is protecting the ball or avoiding turnovers. Empty possessions are the bane of every coach. As has been often said, “100% of your shots not taken don’t go in”. A turnover results in a shot not taken. However, not all turnovers are equal. The fewer possessions that a team has, the more important it is to avoid turnovers, since the opportunities to score for teams that play slow are fewer than teams that play at a high pace.
Thus, the appropriate measure for how well a team protects that ball is not total turnovers. Rather it is what percentage of their total possessions result in turnovers. Specifically, it’s turnovers divided by possessions where possessions are defined as:
Note: Oliver’s weighting factor for free throw attempts is 0.4 which is the number that continues to be used for NBA analysis. Work by John Hollinger and others suggest that the proper factor for college teams is 0.44.
The key here is, specifically, offensive rebounding. If a team is a strong offensive rebounding team they can partially make up for a poor first factor. An offensive rebound gives a team a second chance at scoring. You still have to put the ball in the basket but if you get multiple opportunities to try it during a possession than you can go a long way toward making up for poor shooting. Conversely, limiting your opponent to one and only one opportunity during their possessions is important on the defensive side of the ball.
The proper measure for this isn’t to compare your offensive rebounds with your opponents, it’s to measure what percentage of the rebounding opportunites that presented themselves while you were on offense resulted in your keeping the ball, i.e. it compares your offensive rebounds with your opponents defensive rebounds. The specifics:
The last measure of offensive performance is getting to the foul line. But it’s not just how well do you shoot free throws while you are on the line, it’s how successful are you at getting to the line AND making them. What you would like to see is a high number of free throws made per shot attempt, so the proper stat becomes:
In his original work, which primarily studied NBA teams, Oliver says that relative importance of each of these factors is:
- Shooting (10)
- Turnovers (5-6)
- Offensive Rebounding (4-5)
- Free Throws (2-3)
One thing that shouldn’t be overlooked is that these relative weights will differ by team based on the style of game that they play.
When I do any game analysis, I will always try to base it on Oliver’s Four Factors. Breaking each team down offensive and defensively across these four factors can provide substantial insight into any game.