I’ve never been completely satisfied with the plus/minus system that I have been using, so I decided to do some additional research into the area. I think I’ve found some adjustments that I can make to my methodology that will make the system more meaningful.
One of the issues with the simple plus/minus raw number that I have been reporting is that it can be completely blown out of proportion by one lopsided game. Racking up a huge positive number in any one game can mask many negative performances in other games. For example, every player in the Canisius game recorded a positive number from 18 to 37 points. There’s little doubt that some of the guys season long numbers are heavily waited by that one game – that’s a problem.
What the plus/minus raw number that I have traditionally been reporting represents is how the team did while the player was on the floor. It says nothing about how the team did with the player OFF the floor. The team might be scoring at a plus margin with the player in the game but at an even better margin with him out. You couldn’t tell that from the old way of calculating the number.
The new Plus/Minus Rating number will compensate for that. Simply put, it’s the points delta for the team while the player is on the floor minus the points delta for the team while the player is OFF the floor. If a team plays better with the player off the floor he will have a negative Plus/Minus Rating for that game.
I will report a players Plus/Minus Rating for every game plus total the game ratings to give a Net Score for the season. I’ll also calculate the Net Score per game to balance out the numbers for situations where a player didn’t get into a game.
One thing to keep in mind with this number is that it is really measures what a player does compared to what his replacements do. It shouldn’t necessarily be used to compare two players. However, a player with a large plus number is performing better than his replacements and should be considered a candidate for more playing time while a player with a negative number perhaps should have his time reduced.
I’m also going to make a nomenclature change. In the reports that I’ve presented in the past, I’ve calculated what I called the plus/minus winning percentage. If a player had a positive plus/minus number for a game he was credited for a “win” in my winning percentage calculation (a negative number equated to a loss and a net zero for the game was calculated as half a win and half a loss). I’m going to do the same percentage calculation based on the new version of the plus minus but will no longer use the confusing term “winning percentage”. Rather I’ll refer to the as Plus Games and Minus Games (abbreviated G+ and G-). The percent of games that are Plus Games will be abbreviated as G%.
I will definitely be reporting the individual plus/minus games using this new methodology and will probably do the same for the pairs analysis (I’m still playing with the spreadsheets for the pairs).