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:An extensive survey of features for quality flaw recognition has been provided by Anderka et al. (2012). We selected a subset of these features for our experiments and grouped them into four feature sets in order to determine how well different combinations of features perform in the task.
Category: