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:Examples include Barry (1974), Brown (1976), Bawa, Brown and Klein (1979), Jobson, Korkie, and Ratti (1979), Jobson and Korkie (1980), Jorion (1985; 1986), McKinlay and Pastor (2000), Goldfarb and Iyengar (2003), Ledoit and Wolf (2004), Garlappi, Uppal, and Wang (2007), and Kan and Zhou (2007)…
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