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:However and in contrast to our results, other works demonstrated that the repeated subcutaneous administration of morphine did not induce antihyperalgesic and antiallodynic tolerance after the partial sciatic nerve injury-induced neuropathic pain (Narita et al., 2011; Sounvoravong et al., 2004).
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