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:…theoretically attractive, this is practically unachievable owing to the potentially embarrassing or personal nature of reproductive studies per se (Handelsman et al., 1985), the attitudes of those seeking care (Tielemans et al., 2002) and self-selection of those who are willing to participate…
Category: