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:3 Implementation
3.1 Data pre-processing
Although the WHO database allows for the transmission and storage of large amounts of data for each individual case report, few case reports have even the majority of the fields filled in (Bate et al. 1998).
Category: