“…Historically, the most common statistical method for evaluating the effects of multiple risk factors on long-term survival has been Cox proportional hazards regression analysis [25]. This approach, used in many studies of longterm survival following SCI, allows the simultaneous consideration of main and interactive effects of other known mortality risk factors such as gender, race, cause of injury, education, income, smoking, etc., in addition to age and neurologic status, and can accommodate changes in risk factors over time through the use of time-dependent covariates [11,16,[19][20][21]. However, there are two significant limitations to the use of Cox models.…”