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:A proposed model equation can only be accepted when different inhibitor concentrations are assayed and if consistent results are obtained as follows: the best-fitting model possesses the same number of components with the same amplitudes and kinetic constants for each tested inhibitor concentrations (Estévez and Vilanova 2009).
Category: