Thrombosis-free survival curves (Kaplan-Meier method) of family members without defects (dotted line), with factor V R506Q alone (dashed line), and factor V R506Q with HR2 (continuous line). In all curves each step represents a VT event. Differences between the curves (factor V R506Q with HR2 v individuals with no defects orv factor V R506Q alone) were significant by log-rank test (P < .001 and P = .01, respectively).