Gini coefficient is sometimes used in classification problems. Gini coefficient can be straigh away derived from the AUC ROC number. Gini is nothing but ratio between area between the ROC curve and the diagnol line & the area of the above triangle. Following is the formulae used :
Gini = 2*AUC – 1
Gini above 60% is a good model. For the case in hand we get Gini as 92.7%.