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:Traumatic events were assessed using the WMH version of the WHO Composite International Diagnostic Interview (CIDI) Version 3.0, a fully structured diagnostic interview administered by trained lay interviewers [21], which includes a screen for traumatic events as part of the module for the diagnosis of PTSD.
Category: