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:Because most off-target nicks are not adjacent to each other and do not form DSBs, these nicks are repaired precisely and rarely lead to indels (Ran et al. 2013a; Shen et al. 2014).
Category: