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:Measurements of APP have been used extensively for monitoring health status and disease progression, and in the evaluation of treatment efficacy (Carroll et al., 2004; Sorensen et al., 2006; Pomorska-Mól et al., 2011a).
Category: