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:METHODS A total of 20 PD patients (response rate 71.4%; mean age 64.4 ± 11.6 years) were assessed using the Beliefs about Medicines Questionnaire, Self Efficacy for Managing Chronic Disease Scale, Hospital Anxiety and Depression Scale (HAD) and Kidney Disease Quality of Life-Short Form.
Category: