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:In time-to-event analysis, Cox proportional hazards regression models that controlled for study design were used to estimate crude and adjusted hazard ratios (AHR) and 95% confidence intervals (CI) for covariates of interest [34].
Category: