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:Clinical variables, such as the type of presenting complaint [13], health and mental health status [4, 14, 15], and diagnosis and severity of illness [16, 17, 18] have also been shown to affect the use of psychiatric services.
Category: