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:Suwazono et al.,
2006, Japan
Male employees
in steel industries 2426 shift, 3203 day
Mean age:
Shift 37.7 (SD 8.8) Day 35.1 (SD 9.9)
Rotating
night-shift
Type 2 diabetes HbA1c 6.0% 10 years OR¼ 1.35 (CI 1.05–1.75)
multivariate adj.
Category: