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:The inhibition of down-regulation of HMGA2 by gene knockdown of unrelated ALKs based on the current signaling model [4–7] may be indirect effect, because gene expression was examined at 24 h after ligand stimulation.
Category: