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:‚Ä¶double blind crossover pattern separated by 7 days, which has been previously demonstrated to allow suYcient time to ensure that there are no eVects of previous supplementation on subsequent blood hormone and chemical analysis (Brown et al. 1999, 2000b, 2002; King et al. 1999; Earnest et al. 2000).
Category: