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:Notice that PCA can be seen as the basis of several other multivariate data analysis methods such as PLS (McIntosh et al., 1996; Lobaugh et al., 2001), whereby it is restricted to the brain–behavior covariate matrix.
Category: