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:Further complicating the issue, social desirability, varied interpretations of questions, and problems in recall can impede accurate measurements of risky sexual behavior (Brewer, Garrett, & Kulasingam, 1999; Brody, 1995; Schroder et al., 2003).
Category: