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:Using
the classification system of Zhan et al. [13], the medications listed in Table 1 were further categorized into three groups: medications 1) that should always be avoided (barbiturates, flurazepam, meprobamate, chlorpropamide, meperidine, pentazocine, trimethobenzamide, belladonna alkaloids, dicyclomine, hyoscyamine, propantheline), 2) that are rarely appropriate (chlordiazepoxide, diazepam, propoxyphene, carisoprodol, chlorzoxazone, cyclobenzaprine, metaxalone, methocarbamol) and 3) that have some indications but are often misused (amitriptyline, doxepin, indomethacin, dipyridamole, ticlopidine, methyldopa, reserpine, disopyramide, oxybutynin, chlorpheniramine, cyproheptadine, diphenhydramine, hydroxyzine, promethazine).
Category: