NBA - Home Win Probability Using SRS

The following equations can be used to determine true money-line and true point spreads for the NBA. The basis of them are using Adjusted Simple Rating System (aSRS), which can be calculated by:

 

      Where:

• aSRS = adjusted simple rating system
• G = games played
• SRS = simple rating system

Simple Rating System—from what I've seen—is only published on Basketball-Reference, and is calculated by adding the team's margin of victory and strength of schedule. Justin Kubatko of Statitudes compiled the results of the 1976–1977 through 2012–2013 NBA seasons using aSRS, and created the following logit equation to predict the probability of the home team winning:

      Where:

• e = Euler's number, the base of natural logarithm
• dSRS = Home team's aSRS – Away team's aSRS

This answer will produce a decimal (i.e. 0.5277) which can be multiplied by 100 to get the implied probability (i.e. 52.77%). This implied probability can be converted into a true money-line by using a convertor. Finally, this probability can be converted into a point spread using the following equation:

Sources:
Kubatko, Justin (November 13, 2013). "Home Win Probability Using SRS." Statitudes. Retrieved November 26, 2013.