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:Our findings are supported by a growing number of epidemiological studies showing an association between air pollution exposure and cognitive impairment in the elderly (Chen and Schwartz 2009; Power et al. 2011; Ranft et al. 2009; Wellenius et al. 2012; Weuve et al. 2012a; Chang et al. 2014; Tonne et al. 2014, Ailshire and Crimmings 2014, Ailshire and Clarke 2014) and by toxicological studies suggesting that air pollution has neuropathological effects (Block and Calderón-Garcidueñas
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