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:Homeostatic Model Assessment–Insulin Resistance (HOMA-IR) was calculated as follows: HOMA-IR = fasting glucose value (mg/dl) × fasting insulin value (μU/ml)/405 (Matthews et al. 1985).
Category: