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:Studies by Ross and Lindsay (1965), Sandham (1986), Horswell (1991), Hoenig and Schoener (1992), Ugar and Semb (2001), Giannakari (2004), Rajion et al. (2006), Lima et al. (2009) supported this finding and confirmed the association between upper cervical vertebral anomalies and cleft lip and/or…
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