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:Six papers seemed to specify a rate assuming equality of the experimental and control groups [12,15, 18-21]; seven seemed to specify the control group response rate, πC , assuming inequality [14,15,17,21-25]; and ten did not cite a design rate – in these cases we used the empirical estimate of πC from the paper’s Results section to classify extremity of the rate.
Category: