Empirical Findings
In a logistic regression model, there are two indexes to describe the global fit of the model that represent the proportion of uncertainty of the data explained by the adjusted model. Through analogy with the determination coefficient in the linear regression, they are represented by R2 corresponding to the R2 of Cox and Snell and the R2 of Nagelkerke. The value of the R2 of Cox and Snell has the inconvenience of not reaching the value 1(100%) when the model reproduces the data exactly.