From their page [http://mill.ucsd.edu/index.php?page=Datasets&subpage=Task1 http://mill.ucsd.edu/index.php?page=Datasets&subpage=Tas...]: Scoring Predictions

From their page [http://mill.ucsd.edu/index.php?page=Datasets&subpage=Task1 http://mill.ucsd.edu/index.php?page=Datasets&subpage=Tas...]: Scoring Predictions Evaluation Metric: The evaluation metric for the E-commerce Transaction Anomaly Classification (Easy) is lift at 20%. If S is the 20% of examples that you think are most likely to have a positive label, then the lift at 20% is proportional to the number of positive examples in S.