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:It had 2565 (2805) states optimized with the variational Bayesian estimation and clustering (VBEC) technique (Watanabe et al., 2006) and each state had 32 (32) -mixture Gaussian pdfs.
Category: