So I was lurking on one of the Facebook AT Hiking pages and someone asked how to get over their fear of bears. I offered a statistical argument that people aren't generally afraid to drive cars even though there are about as many people killed per day in auto accidents as there are people killed by black bears per century. Someone posted a terse retort that because there are many more drivers than hikers, that was a false equivalency. A minor flame war ensued (in which I did not participate), but it got me thinking. First, why did I get involved in such a pointless FB posting. Second (and more interestingly), could I statistically address the issue there are more drivers than hikers and normalize the data to make a fair comparison. So......
According to the NHTSA there are on average about 97 deaths per day from auto accidents in the US. On a given day there will be 8.5 billion miles driven. But it doesn't seem to me that comparing hiking miles to driving miles is a fair comparison. It seems more reasonable to compare the auto risk per day of driving to the bear risk per day of hiking. I put about 15,000 miles on my cars per year which works out to about 41 miles/day on average so at that rate, the 8.5 billion total miles of driving that generates 97 deaths represents about 210 million people driving 41 miles per day.
Now for bear and hiking data. There have been 5 fatal bear attacks in the eastern US (AT states) since 1900 or 0.00012 deaths per day. If I knew the number of people hiking in the woods each day in the eastern US I could get a fair comparison of the bear deaths per hiker to the auto deaths rate per driver from above. However the number of hikers is hard to come by and would be a rough estimate at best. But what we can do is assume that the auto and bear risks are the same and that the auto number is higher simply because there are more drivers. So if you set up the equation (hikers per bear death = drivers per auto death), plug in the three numbers we know (bear deaths = 0.00012 deaths per day, auto deaths = 97 deaths per day, number of drivers = 210 million) and solve for the number we don't know we calculate there must be 250 hikers. In other words if the chance of being killed by a bear when spending a day hiking in the eastern US were same as being killed in a car accident while driving 41 miles, then there would have to be 250 people hiking each day in the Eastern US. However we know that there are a lot more than 250 hikers per day out in the woods of the eastern US. In fact the AT thru hikers represent more than 250 hikers per day over the course of the year. If you want to assume there are 100 times this many hikers per day then you have to conclude the chances of being killed by a bear are 100 times smaller than being killed in a car accident.
According to the NHTSA there are on average about 97 deaths per day from auto accidents in the US. On a given day there will be 8.5 billion miles driven. But it doesn't seem to me that comparing hiking miles to driving miles is a fair comparison. It seems more reasonable to compare the auto risk per day of driving to the bear risk per day of hiking. I put about 15,000 miles on my cars per year which works out to about 41 miles/day on average so at that rate, the 8.5 billion total miles of driving that generates 97 deaths represents about 210 million people driving 41 miles per day.
Now for bear and hiking data. There have been 5 fatal bear attacks in the eastern US (AT states) since 1900 or 0.00012 deaths per day. If I knew the number of people hiking in the woods each day in the eastern US I could get a fair comparison of the bear deaths per hiker to the auto deaths rate per driver from above. However the number of hikers is hard to come by and would be a rough estimate at best. But what we can do is assume that the auto and bear risks are the same and that the auto number is higher simply because there are more drivers. So if you set up the equation (hikers per bear death = drivers per auto death), plug in the three numbers we know (bear deaths = 0.00012 deaths per day, auto deaths = 97 deaths per day, number of drivers = 210 million) and solve for the number we don't know we calculate there must be 250 hikers. In other words if the chance of being killed by a bear when spending a day hiking in the eastern US were same as being killed in a car accident while driving 41 miles, then there would have to be 250 people hiking each day in the Eastern US. However we know that there are a lot more than 250 hikers per day out in the woods of the eastern US. In fact the AT thru hikers represent more than 250 hikers per day over the course of the year. If you want to assume there are 100 times this many hikers per day then you have to conclude the chances of being killed by a bear are 100 times smaller than being killed in a car accident.