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 contradictory findings that human p60 binds stably to microtubules in vitro but never co-localizes with microtubules in vivo (McNally and Thomas, 1998) suggested that katanin might interact transiently with microtubules in vivo.
Category: