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:Kongkam et al. 2009 (40)
Case series report Morphine and other opioid and/or nonopioid drugs
Pump dislodgment/migration in 2 of 13 patients (15.4
Category: