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:This differs from the results of previous studies where learning affects both searching and handling efficiency (Werner et al. 1981; Dill 1983; Ehlinger 1989a, b; Croy and Hughes 1991).
Category: