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:[33] In order to enrich the CIS group for patients at highest risk of progressing to MS, [34] CIS patients with at least one T2 hyperintensity typical of demyelination on conventional brain MRI were considered to be ‘‘high-risk’’ and were included for analysis.
Category: