International Conference on Applications of Statistics and Probability in Civil Engineering (ICASP) (12th : 2015)

The effect of under-reporting of non-fatal involvements in snow avalanches on vulnerability Jamieson, Bruce; Jones, Alan S. T.


For a person caught in a snow avalanche of specified magnitude, vulnerability is probability death. In North America and most alpine countries, most fatalities due to snow avalanches occur during recreation and are thus a voluntary risk. The previously reported vulnerability of recreationists to snow avalanches is typically in the range of 0.1 to 0.25, which is also applied to workers travelling on skis and snowmobiles in uncontrolled areas (backcountry). This is the base rate (prior probability) for many studies of survival factors such as use of specific rescue devices, burial depth, etc. Most studies of people caught in avalanches assume that all non-fatal involvements are reported. However, in a recent Canadian study, Jamieson and Jones (2012) argued that only 5 to 10% of persons caught but not killed by an avalanche during recreation are reported. This results in potential overestimation of vulnerability by a factor of about 10 or greater. Such uncertainty in the base rate can undermine statistical studies of survival factors. We review the assumed reporting rates from international studies and their calculated vulnerability rates from snow avalanches in uncontrolled terrain. We conducted a survey of those who had been caught in an avalanche, which indicated that 11% of non-fatal involvements are reported in Canada. We discuss both positive and negative biases in our survey results. Based on Canadian data, we conclude that the vulnerability for persons travelling on skis or snowmobilers and caught in a potentially fatal avalanche is approximately 0.03. This revised base rate may prove useful in studies of rescue devices, burial depths, public avalanche education programs, and policies concerning risk management and resource allocation.

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