Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:The ROC curve was calculated by varying the probability values (i.e., the decision criterion) of error classification from 0% to 100% and plotting the associated true positives and false positives (Fawcett, 2006; Macmillan & Creelman, 2005).
Category: