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:(3)
It worth noting that the optimal conductance parameter can be estimated by iterative methods (Tsiotsios and Petrou, 2013), however, we have a fixed κ based on the previous optimization in MRI and DTI studies (Moraschi et al., 2010; Senra et al., 2015).
Category: