The Four Factors

Dean Oliver is to basketball as Bill James is to baseball.  They both revolutionized the way we use stats to look at games.  Basketball On Paper is Dean's book.  Anyways, he spent a lot of time analyzing games and stats and came up with this methodology.  The Four Factors represent the most important statistical keys for a team winning or losing.  These factors are also tempo-free.  Tempo-free is an attempt to show how efficient a team is regardless of the fact of how fast or slow they play, ie. how many possessions they have in a game.

So to begin every game you must calculate the number of possessions.  This formula is:  FGA-OR+TO+.475*FTA.  Alright so this is getting at calculating the number of times the ball changes hands by using all the standard info from a box score.  So FGA-OR gives you the number of shots you either made or the other team rebounded - thus resulting in a change.  Then you add TO obviously a case where a change occurs.  Then you add .475*FTA.  This guy Ken Pomeroy watched a crapload of games (by the way kenpom.com is the place I get a lot of stats from and a fantastic site) and figured out that 47.5% of all FTA's result in a change of possession.  So that part calculates how often a FTA results in a change of possession.  So there you have the formula for possessions.  By the way you use the stats from each team in terms of OR, TO, etc. and then divide the number by 2.

Rating, either defensive or offensive, is again a calculation based on how efficient you are per possession.  The formula is simple.  Take the number of points/by the number of possessions then multiply by 100.  So, the rating tells you how many points you would score or give up per 100 possessions.

eFG%  is a weighted FG% that takes into consideration that a shot from 3 that is made is worth more than a shot from 2.  The logic is pretty simple then that shots from 3 should count more.  Formula is FGM+.5*3FGM/FGA.  So total shots made + half a point added for each 3 pointer made / total shot attempts.

TO%  again another tempo free stat.  So instead of saying Team A averages 18 TO's a game it calculates how many possessions end in TO's.  Because 18 TO's for a team that plays fast means less than 18 TO's for a team that plays slower and has fewer possessions.  Formula is:  TO/possessions

OR% This stat explains how often you grab the available offensive rebound.  Same logic can be applied as the TO% but the formula is different:  OR/OR+DR(of the opposing team).  So in order to calculate the rate at which you grab offensive glass you divide by the number of your offensive boards and the opponents defensive boards.  That addition gives you the total number of opportunities you have to grab an offensive board.  So dividing your OR by that number gives you the rate/% you get OR.

FTA/FGA is the formula.  It is actually called the Free Throw rate.  This measures a players or a teams ability to get to the line relative to how often the attempt to score.  So you divide FTA/FGa*100 and that is your rate.

There are many other tempo free stats but these are the basics and for now enough explanation.