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:Some strategies have been proposed adjusting the decision tree induction to be more sensitive to imbalanced class distribution (Hulse et al. 2007):
• For imbalanced class distribution, pruning a decision tree can over generalize and completely ignore the positive class, and so decision trees are…
Category: