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:For instance, the use of methamphetamine (MA), a highly neurotoxic stimulant, during adolescence may be associated with cognitive (King et al. 2010) and brain structural deficits (Lyoo et al. 2015).
Category: