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:…analysis on diagnosis of HD in PD and employed a variety of machine learning techniques and classification analyses to introduce the acoustic analysis as a non-invasive diagnostic marker of PD (Novotny et al. 2014; Orozco-Arroyave et al. 2013a, b; Rusz et al. 2011, 2013b; Smekal et al. 2015).
Category: