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:…different site between SMN1 and SMN2 is shown in black ic position; REF, reference allele of the SNPs; ALT, alternative allele of the SNPs; H,
widely applied in clinics (Handyside, 2011, 2013; Tan et al., 2013; Jones et al., 2014; Fan et al., 2015; Lukaszuk et al., 2015b; Zimmerman et al., 2016).
Category: