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:…sample into two groups comparing those who displayed high levels of behavior problems as indexed by the Eyberg Problem or Intensity factor, using previously validated cut-off scores and mirroring the criteria applied during recruitment for the study (Burns and Patterson 2001; Dishion et al. 2008).
Category: