# Square6 evans et al in their response accepts that

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square6 Evans et al in their response accepts that disaggregation of Barnett is sensible and that Barnett identified a safer mode of air travel (i.e. by jet planes) however Evans et al’s point is that there are some individuals who have lower expected fatality rates on some trips if they drive rather than fly even though for the overall population fatality risk in driving exceeds that in flying.

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9 Nonstop flying is safer than driving square6 Air fatality rate for non-stop flights is substantially less than the rate derived by Evans et al. square6 As air fatality rate per flight is assumed to be independent of the length of the trip, air travel calculations that avoid passenger miles of travel are more appropriate square6 The conclusion of this study is that driving appears to be safer than flying only for substantially shorter distances than suggested by the analysis of Evans et al. Nonstop flying is safer than driving square6 Evans et al started with a fatality rate per billion passenger miles of 0.55 and 880 miles average length of a trip to reach the 484 fatalities per billion passenger flights value. But the average nonstop flight length is 551 miles hence the correct value should be 302 fatalities per billion passenger nonstop flights. square6 The comparison between the safety of air travel and automobile travel is complicated by the problem that segments are the logical unit of measure for one and distance for the other.
10 Nonstop flying is safer than driving square6 For the period of 1978-1987, there were 1332 passenger fatalities, 55,267,218 nonstop segments and the average number of passengers per nonstop segment was 98.8 1332/(55,267,218*98.8)=244*10 -9 fatalities per billion passenger flight segments Nonstop flying is safer than driving Probability of a fatality does not actually increase linearly with driving distance Probability of a fatality does not actually increase linearly with number of flight segments

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11 Nonstop flying is safer than driving P(f2)=P(f1)+P(f1)[1-P(f1)] P(f1)=Probability of fatality for a one segment flight P(f2)=Probability of fatality for a two segment flight P(f)=1-e -kd d being trip distance and k a constant estimated by the ratio of total driver fatalities to total driver miles General critique for flying against driving risk analysis square6 Parameter estimation ignores possible interaction among factors square6 Analysis ignores trip to airport, differences in carriers, non-interstate portion of drive, differences in route lengths square6 Auto risk analysis assumes a multiplicative model square6 Analysis ignores non-fatal accidents which occur 70 times as frequently as fatal auto accidents but less so for airlines
12 Alternative Models of Risks A hard question is how does one know which mathematical model is most appropriate to model different risks . The question is often hard because there is no clear cut answer. Decisions are often reached by subjective considerations and compromise between different issues . Several models may appear to be equally valid; sometimes one model may appear to fit better than an alternative model which has better theoretical justification. Alternative Models of Risks When selecting a functional form for the model, one often considers matters of convenience , data sufficiency and reasonableness .

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• Spring '10
• fernando
• Evans, air travel, fatality rate

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