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:Studies were included according to the following inclusion criteria: (1) prospective or retrospective cohort studies; (2) inclusion of patients with ESRD undergoing hemodialysis or peritoneal dialysis; (3) baseline serum ALP levels as exposure; and (4) provided multiple adjusted odds ratio (OR) or hazard ratio (HR) and 95% confidence interval (CI) of cardiovascular or all-cause mortality comparing the highest with the reference lower serum ALP levels.
Category: