roc_auc score GridSearch I am experimenting with xgboost. 

I ran GridSearchCV with score='roc_auc' on xgboost. The best classificator scored ~0.935 (this is what I read from GS output). But now when I run best classificator on the same data:

roc_auc_score(Y, clf_best_xgb.predict(X))


it gives me score ~0.878

Could you tell me how the score is evaluated in both cases? Thanks
Try using predict_proba instead of predict as below. It should give you the same number.

roc_auc_score(Y, clf_best_xgb.predict_proba(X)[:,1]) 

When we compute AUC, most of time people will use the probability instead of the actual classs.