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:Figure 1 (top) shows the data from McCarthy and Davison (1984), which arranged four stimulus discriminability levels, and for each level, arranged three different reinforcer frequency ratios (4:1, 1:1, and 1:4).
Category: