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:The transfection method using adenovirus conjugated to poly-L-lysine and the techniques used to expose cells to laminar shear stress with the use of a parallel-plate shear chamber and flow loop have been described elsewhere (15).
Category: