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:Results of the optimal TLC thresholds and the corresponding combinations of sensitivity and specificity from the outpatient study and the results of the literature review were quite similar, while both were different from those reported among HIV-infected populations in other countries [19–22].
Category: