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:The joint distribution differs significantly from the earlier distribution, developed in Forest et al. (2002) and used in Webster et al. (2003), because the model simulations for the twentieth century used by Forest et al. (2006, 2008) include several additional forcings.
Category: