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:29 The 40% fT>MIC target was chosen because it represents maximum bactericidal activity in animal and in vitro studies.(5) The 60% fT>MIC target was chosen because a recent study in patients with lower respiratory tract infections found a significant relationship between microbiologic response and an fT>MIC of 54%.
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