How is 2-year mortality risk adjusted?

The model for two-year mortality additionally includes interactions between follow-up period (0-3 months after surgery vs. 3-24 months after surgery) and all of the risk factors.

This allows risk factors to have a different effect shortly after surgery and in the longer term. For example, the effect of ASA grade is much larger peri-operatively than in the longer-term, whilst cancer stage has a much larger impact on longer-term than short-term mortality.