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:Some investigators have noted an association of Pg antibodies with anti-CCP antibody levels, but not with RF values [14,15], whereas others found a correlation of Pg immunoglobulin G (IgG) antibodies with RF levels, but not with CCP antibody values [5,16].
Category: