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:More recent examples for maize include Labate et al. (1999) and Coque and Gallais (2006) for yield selection, and Wisser et al. (2008) for disease resistance, while De Koeyer et al. (2001) examined yield in oats.
Category: