The designation as primary or secon

The designation as primary or secondary was subjective, based on discussion and consensus of the team. Two guidelines influenced the choice:  A primary factor more likely seems a necessary condition for a fatality. Take it away and the crash would probably not have been fatal. Secondary factors increase risk, and may even have been the last straw in a specific case, but not so evidently as a primary factor.  A primary factor tends to be an original cause; secondary factors may be consequences of a primary factor. For example, if a car severely underrides a heavy trailer, uppercompartment intrusion resulting in fatal head injuries is an almost inevitable consequence. Underride is the primary factor; upper-compartment intrusion is the secondary factor. The above are just guidelines – the team designated the primary factors based on what they believed best described what happened in a particular crash. There can be two or more primary factors if both are necessary for the crash to be fatal. For example, consider a centered impact with a tree, resulting in late deployment and fatal injuries to an elderly driver. If this elderly driver would have likely survived a timely deployment, and a 30-year-old driver would have survived even this late deployment, then “impact with tall, narrow object” and “occupant’s age” should both be primary factors (because if either of the two factors had not been present, the crash would likely not have been fatal). If the driver had been even older and would likely not have survived even a timely deployment, only “occupant’s age” should be a primary factor (and “tall, narrow object” would have been secondary, because the impact would likely have been fatal for this driver even with a wide object). But if the crash had been more severe and even a 30-year-old driver would not have survived the late deployment, only “impact with tall, narrow object” should be a primary factor (and “occupant’s age” would have been secondary, because the crash would likely have been fatal even for the younger driver). If the same crash had been yet even more severe, to the point where a 30-year-old driver would not likely survive a timely deployment, “exceedingly severe crash” might become the single primary factor (and “occupant’s age” and “tall, narrow object” would have become secondary, because the crash would likely have been fatal without either of them). Of course, nobody knows for sure exactly what the last straw was in the actual crash, let alone in the hypothetical situations where one factor is removed, so all designations have to be based on the team’s judgment and consensus.