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 is in agreement with previous work investigating the effects of rTMS on simple motor behavior (Wassermann et al., 1996; Chen et al., 1997; Pascual Leone et al., 1998; Muellbacher et al., 2000; Rossi et al., 2000).
Category: