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 pCEFLHA-HMGA1, pCEFL-HA-HMGA2, pCEFL-HA-HMGA1 (1–43) and pCEFL-HA-HMGA2 (1–73) vectors were previously described (Fedele et al., 2006; Pierantoni et al., 2001; Pentimalli et al., 2008).
Category: