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:Similar observations have been made in the USA, where gonorrhoea and other sexually transmitted infections (STIs) have been shown in multiple studies to be concentrated in certain geographical areas (Rothenberg 1983; Potterat et al. 1985; Bernstein et al. 2004; Kerani et al. 2005).
Category: