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:We perform extensive comparative studies with a number of state-of-the-art algorithms as benchmarks: PA [Crammer et al., 2006], SCW [Wang et al., 2012], OGD [Zinkevich, 2003], AROW [Crammer et al., 2009; Crammer et al., 2013] (we use the implementation in LIBOL library [Hoi et al., 2014] for these algorithms,
default value for parameters are used if available), and Online Bagging [Oza and Russell, 2005] (we use the implementation in MOA library [Bifet et al., 2010]).
Category: