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 has been improved by means of techniques and instruments of data acquisition: particularly, through the development of statistical packages applied to the different factors as well as through GIS softwares, used for the management and processing of georeferenced data for large areas (Johnston, 1998; Meijerink et al., 2003; Daniels, 2003).
Category: