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, the results of studies by Sajedi and Alizad,[20] Ghahramani
and Tavakolizade,[21] Amir Ali Akbari et al.,[15] Nouhjah et al.,[30] Ozbek et al.,[39] Hediger et al.,[18] Potijk et al.[25] and Richter and Janson[24] are in contradiction with the above results.
Category: