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:Consistent with previous results (Koroch et al. 2002; Liu et al. 2002; Staniszewska et al. 2003; Washida et al. 2004), the addition of IBA at optimum levels enhanced the growth of HRC of Echinacea but had no effect on the production of secondary metabolites.
Category: