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:Parameters are chosen as in Abeler et al. (2010) such that higher effort by agents is always socially efficient, but principals and agents have immediate material incentives to free-ride and avoid the cost of paying high wages or effort costs, respectively.
Category: