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:This model of practice is common for home intravenous therapy programmes in the UK (Nathwani 1995, , Nathwani and Davey 1996, Kayley 2003), however; recently this model has been revaluated (Laupland et al 2002, Cooper 2003).
Category: