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¶& Pearson (1991) found no separation by different size classes of mayfly species and different types of substratum, our results suggest the presence of a sizerelated shift in habitat use, as identified in many other studies (i.e. Pringle, 1982; Williams & Moore, 1986; Osborne & Herricks, 1987).
Category: