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:The first type includes blind source separation algorithms like independent component analysis and principal component analysis (PCA)[26, 40, 27, 32, 12, 52], spatiotemporal QRST cancellation [49, 30, 6], and adaptive filtering with its variations [50, 9, 37, 51].
Category: