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:Usually PUVA is between 90° and 100° [31], however, in our study, the results showed that PUVA in SUI patients was higher than healthy women no matter at resting state or increased abdominal pressure state, indicating that the urethra of patients showed shortening trend which was consistent with the morphological change of urethra at early stage of urination.
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