To illustrate the difference between per game production, per minute rates, and tempo-free statistics we'll start with a question: who was the better rebounder in 2011 between these two players?
|Player A||6.3 (17)
2011 rebounding numbers for two WNBA players with league ranks in parentheses.
Rebounds per game is a pretty straightforward productivity metric - it's simply the number of rebounds each player got per game. Rebounds per 36 minutes is a per minute rate: rebounds per minute multiplied by 36 to approximate what kind of numbers players would put up if we held everyone's minutes equivalent to that of a star. Using the per minute stats we see that Player B has closed the gap a bit on Player A, whose 6.3 rebounding average is a top 20 per game production rate.
Rebounding percentage turns things around a bit though and there are a potential few reasons for that. First, Player A was Atlanta Dream forward Sancho Lyttle while Player B was then-Seattle Storm forward Le'coe Willingham. The Dream were the fastest-paced team in the league (81.2 possessions per game) and the Storm the slowest (72.7 poss/g). That means that in addition to Lyttle playing more minutes per game than Willingham last season (26.2 and 19.1, respectively) she was also on a team that likely had more opportunities to rebound during that time, which inflates both her per game productivity and her per minute rebounding rate a bit in comparison to a player on a slower team. In contrast, rebounding percentage is a tempo-free statistic that measures a player's rebounding rate by possession, which therefore holds pace of play (or tempo) constant.
To be honest, there aren't many situations where there's even this small of a difference better per minute and tempo free statistics in understanding an individual player's rebounding ability, particularly not on the pro level where there's less variance between both competition and tempo. But it helps to understand why this distinction is important: although per minute rates have been found to be reliable in projecting a player's ability, there are cases where pace inflates that number when context is taken into account.
For more on tempo-free statistics, visit Basketball-Reference.com's primer on the Four Factors.