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:Previous studies have demonstrated that ixazomib has a shorter proteasome dissociation half-life, a larger blood volume distribution at a steady state, and a greater and more constant biodistribution than bortezomib [4, 14, 17].
Category: