It is a measure of goodness of fit in logistic regression analysis. It is a modification of the Cox and Snell R Square, which is derived from the likelihood ratio test statistic.
Nagelkerke R Square ranges from 0 to 1, with values closer to 1 indicating a better fit of the model. However, unlike in linear regression analysis, where R Square can be interpreted as the proportion of variance explained by the model, Nagelkerke R Square cannot be interpreted as easily.
A common rule of thumb is to interpret it, a value of 0.2 or less indicates a weak relationship between the predictors and the outcome.
A value of 0.2 to 0.4 indicates a moderate relationship.
A value of 0.4 or higher indicates a strong relationship.
However, it's important to note that the interpretation of Nagelkerke R Square should be taken with caution and should be supplemented by other measures of model fit, such as the Hosmer-Lemeshow test, AIC, or BIC. Additionally, it's essential to consider the practical significance of the relationship between the predictors and the outcome, rather than solely relying on statistical significance or goodness of fit measures.