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:Today, naltrexone is often considered an effective and recommendable medication for gambling addiction (Grant et al., 2003; Kim, Grant, Adson, & Shin, 2001; National Center for Responsible Gambling [NCRG], 2009; Problem Gambling Research and Treatment Center, 2011).
Category: