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:P-VS plots of SA1 from 11 to 60 GPa are fitted with a fourth order polynomial (R 2 = 0.9933) and P-VS plots of SA2 from 10 to 59 GPa are fitted with a quadratic function (R2 = 0.9957)
also observed in SiO2 glass (Murakami and Bass 2010) and MgSiO3 glass (Murakami and Bass 2011).
Category: