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:FIS quantifies the deviation from HWE with negative values indicating an excess of heterozygotes, and positive values indicating an excess of homozygotes (see de Meeûs et al., 2007a for a thorough explanation).
Category: