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:Whereas Lorden used crude upper bounds for the Type I error probability that are too conservative for practical applications, Bartroff and Lai (2008) overcome this difficulty by developing numerical methods to compute the Type I error probability and also extended the three-stage test to…
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