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:In a similar way, several authors using flow cytometry, RAPD or RFLP also failed to observe somaclonal variations in various species (Pinto et al. 2004, Saker et al. 2005, Latto et al. 2006, Rady 2006, Loureiro et al. 2007).
Category: