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:A method based on optimizing the training data likelihood, such as Morfessor (Creutz and Lagus, 2002; Creutz and Lagus, 2007; Virpioja et al., 2013), ensures that common phenomena are modeled more accurately, for example by using full forms for highly-frequent words even if they consist of multiple morphemes.
Category: