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:Based on collection of multiple proxy measures of the likelihood of exposure to infectious microbes, a pathogen score was constructed using the mean value of five interviewer-assigned variables, each scored on a 3point scale (0=low exposure, 1=moderate, and 2=high): (1) cleanliness of the food preparation area, (2) means of garbage disposal, (3) presence of excrement near the house, (4) level of garbage, and (5) excrement present in the neighborhood surrounding the household [9].
Category: