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:The validate the effectiveness of the proposed Sr-UDFS, we compare it with several state-of-the-art unsupervised feature selection methods, which includes LapScore (He, Cai, and Niyogi 2006), SPFS (Zhao et al. 2013), UDFS (Yang et al. 2011), MCFS (Cai, Zhang, and He 2010), RUFS (Qian and Zhai 2013), and JELSR (Hou et al. 2014).
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