To Avoid Overfitting Data, What Should be my Rule of Thumb for the Number of Data Points per Variable?

I am currently conducting some regression analysis to predict sales, and I currently have about 45 data points and have collected a lot of potential predictor variables. However, I am weary that I will overfit the data, so I'm wondering...is there a rule of thumb as to how many variables can be assigned given a number of data points, without danger of over-fitting the data? Thanks!

Amnesiac2011-04-18T10:58:34Z

Favorite Answer

Adjusted R^2 is a really useful tool in this situation. It is very similar to R^2 of simple OLS regressions, but it punishes the excessive use of predictor variables:

http://en.wikipedia.org/wiki/R-squared#Adjusted_R2