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:In addition, I followed the approach pioneered by Brownlee et al. (1969) and Novotny et al. (1986, 1990b) and compiled examples of differences in composition between secretions (in the broadest sense, i.e. including urine, faeces, breath etc.) from different categories of mammal, (for example,…
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