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:…can be used to determine parameter values of the Farquhar model (Farquhar et al., 1980), and
leaf venation, which has recently been defined in a
consistent way and appears to be correlated with
other leaf functional traits (Sack & Frole, 2006; Brodribb
et al., 2007; Blonder et al., 2011).
Category: