G Statistic
Perhaps the most straightforward measure of a goodness of fit is the G statistic, also refer to as the “likelihood ratio test.” It is a close analogue to the F statistic for linear regression. Both the F statistic and the G statistic measure a difference in deviance between two models. For logistic regression, the deviance of a model is defined as: 
To determine the overall significance for a model using the G statistic, the deviance for the model and the deviance for the intercept-only model are subtracted. The larger the difference, the greater the evidence that the model is significant. The G statistic follows a chi-squared distribution with p – 1 degrees of freedom, where p is the number of parameters in the model. Significance tests based on this distribution are supported in the Business Analysis Module.
