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:This is also indicative of the results of Kerzenmacher and Gardiner (1998), who applied an inversion method on data from a spruce forest and obtained a CD = 0.2 for the stem region (below 8 m) and a CD = 0.1 for the crown region (above 8 m), i.e. a Pm of 2.
Category: