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:The same threshold pH has been measured for SFV-induced cell fusion (White et al., 1981) and for the bypass of chloroquine, methylamine and NH4C1 inhibition of infection (White et al., 1980).
Category: