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:The glucagon (1–29) concentration was measured by RIA using two types of kit: EURIA-Glucagon (R-E; EuroDiagnostica, Malm€o, Sweden) and Glucagon RIA Kit (R-M; Millipore, Billerica, MA, USA).
Category: