# What is the range of the predictor function in logistic regression?

Is the predictor function in logistic regression a function of the dot product of the parameter vector and the feature vector onto a real value between zero and one? If I'm getting dot products outside of that interval, does that mean my parameter vector is bad?

Thanks

## 1 Answer

In Logistic regression, the result of the linear predictor (g(x)) is from negative infinite to positive infinite.

Then the result of (pi(x)) ranges from 0 to 1 via the link function. This is the definition.

• Great, thanks! For future readers, once you've done the dot product to get a number (which is really the Y coordinate in linear space... the answer to a linear regression problem in terms of log-odds) you transform it back into probability space by doing the following (where p is your answer): exp(p) / (1 + exp(p) ) . The resulting answer should be between 0 and 1. – Walrus the Cat Sep 5 '13 at 9:42