I think we have to give the on-court and off-court numbers the same weight. If he did not do so, I am not sure how we would interpret the plus / minus rating.
Making the measure a per 100 possessions measure it's better rather than per 48 minutes: that's means, it's a very good thing anytime we are able to remove the effect of pace.

This post RESUMES the topic.

The eBA basketball Statistics Creative Analysis System tries to compare team success to individual performance, applying reasonably simple methods.
 
If we want to apply the Plus / Minus Ratings to suggest how a certain sequence of players would perform on the floor against an average opponent, we must determine the sum of each of the five players. We must perform the total sum of all of them and no average them. So the team's average plus / minus needs an adjustment be added, which is explained at the eBA System.
 
We must take into account, using the Plus / Minus Ratings that the overall debate about this rate has dismissed the effect of opponent strength because + / - rate doesn't measure player combinations for the opponents. On the other hand, there is no way to recognize between players who have good individual but bad team numbers, opposed to players with bad individual statistics but good + / - ratings.
 
The suggestion about giving on-court and off-court numbers different weights doesn't resolve this rates problems, because it would give us a rate too contingent on the overall grade of excellence worth of the player's team and in most cases this will have a very minor effect.

So, the real method for efficient results is to refrain from applying the Plus / Minus Ratings exclusively,  without any other method being involved, as a possession based method, for example.
 
As said, resuming, the Plus / Minus rating determines the dimension of the statistical norm difference in team accomplishment when a player is on the court opposed to when he is not. We must concede the validity of the difference in quality of the players that a given player plays with and against, when he is on and off the court. Only when they are the same, or almost the same, the Plus / Minus Ratings will determine the dimension of that given player effect on team's winning percentage compared to that team's average. 

   Jean Louis Trezeguet -  ebastats - the basketball statistics forum

This post resumes this topic and will be completed at the "Statistics" chapter of the eBA basketball Statistics Analysis System.  Another basketball statistics topics you'll find at the basketball Statistics Discussions section of our eBA Stats.com site.