A micromort is a unit of risk measuring a one-in-a-million probability of death (from micro- and mortality). Micromorts can be used to measure riskiness of various day-to-day activities. A microprobability is a one-in-a million chance of some event; thus a micromort is the microprobability of death. The micromort concept was introduced by Ronald A. Howard who pioneered the modern practice of decision analysis.
Micromorts for future activities can only be rough assessments as specific circumstances will always have an impact. However past historical rates of events can be used to provide a ball-park, average figure.
|Death from||Context||Time period||N deaths||N population||Micromorts per unit of exposure||Reference|
|All causes||England and Wales||2012||499,331||56,567,000||24 per day
8,800 per year
|ONS Deaths Table 5.|
|All causes||US||2010||2,468,435||308,500,000||22 per day
8,000 per year
|CDC Deaths Table 18.|
|Non-natural cause||England and Wales||2012||17,462||56,567,000||0.8 per day
300 per year
|ONS Deaths Table 5.19.|
|Non-natural cause||US||2010||180,000||308,500,000||1.6 per day
580 per year
|CDC Deaths Table 18|
|Non-natural cause (excluding suicide)||England and Wales||2012||12,955||56,567,000||0.6 per day
230 per year
|Non-natural cause (excluding suicide)||US||2010||142,000||308,500,000||1.3 per day
460 per year
|CDC Deaths Table 18.|
|All causes - first day of life||England and Wales||2007||430 per first day of life||Walker, 2014|
|All causes - first year of life||US||2013||16.7 per day
6100 per year
|CDC Life Tables
Blastland & Spiegelhalter, 2014
|Murder/homicide||England and Wales||2012/13||551||56,567,000||10 per year||ONS Crime|
|Murder and non-negligent manslaughter||US||2012||14,173||292,000,000||48 per year||FBI Table 16|
Leisure and sport
|Death from||Context||Time period||N deaths||N exposure||Micromorts per unit of exposure||Reference|
|Scuba diving||UK: BSAC members||1998-2009||75||14,000,000 dives||5 per dive||BSAC|
|Scuba diving||UK: non-BSAC||1998-2009||122||12,000,000 dives||10 per dive||BSAC|
|Scuba diving||US - insured members of DAN||2000-2006||187||1,131,367 members||164 year as member of DAN
5 per dive
|Skiing||US||2008/9||39||57,000,000 days skiing||0.7 per day||Ski-injury.com|
|Skydiving||US||2008-2013||135||15,300,000 jumps||9 per jump||USPA|
|Skydiving||UK||1994-2013||41||4864268 jumps||8 per jump||BPA|
|Running marathon||US||1975-2004||26||3300000 runs||7 per run||Kipps C 2011|
|Base-jumping||Kjerag Massif, Norway||1995-2005||9||20,850 jumps||430 per jump||Soreide 2007|
|Mountaineering||Ascent to Mt. Everest||1922-2012||223||5656 ascents||39427 per ascent||NASA 2013|
Activities that increase the death risk by roughly one micromort, and their associated cause of death:
- Travelling 6 miles by motorbike (accident)
- Travelling 17 miles by walking (accident)
- Travelling 10 miles (or 20 miles) by bicycle (accident)
- Travelling 230 miles (370 km) by car (accident) (or 250 miles)
- Travelling 1000 miles (1600 km) by jet (accident)
- Travelling 6000 miles (9656 km) by train (accident)
- Travelling 12,000 miles (19,000 km) by jet in the United States (terrorism)
Increase in death risk for other activities on a per event basis:
Value of a micromort
Willingness to pay
An application of micromorts is measuring the value that humans place on risk: for example, one can consider the amount of money one would have to pay a person to get him or her to accept a one-in-a-million chance of death (or conversely the amount that someone might be willing to pay to avoid a one-in-a-million chance of death). When put thus, people claim a high number but when inferred from their day-to-day actions (e.g., how much they are willing to pay for safety features on cars) a typical value is around $50 (in 2009). However utility functions are often not linear, i.e. the more a person has already spent on their safety the less they are willing to spend to further increase their safety. Therefore the $50 valuation should not be taken to mean that a human life (1 million micromorts) is valued at $50,000,000. Furthermore the local linearity of any utility curve means that the micromort is useful for small incremental risks and rewards, not necessarily for large risks.
Value of a statistical life
Government agencies use a nominal Value of a Statistical Life (VSL) - or Value for Preventing a Fatality (VPF) - to evaluate the cost-effectiveness of expenditure on safeguards. For example, in the UK the VSL stands at £1.6 million for road improvements. Since road improvements have the effect of lowering the risk of large numbers of people by a small amount, the UK Department of Transport essentially prices a reduction of 1 Micromort at £1.60 (US$2.70). The US Department of Transportation uses a VSL of US$6.2 million, pricing a Micromort at US$6.2 .
Micromorts are best used to measure the size of acute risks, i.e. immediate deaths. Risks from lifestyle, exposure to air pollution and so on are chronic risks, in that they do not kill you straight away, but reduce your life expectancy. Ron Howard included such risks  in his original 1979 work, for example an additional one micromort from -
- Drinking 0.5 liter of wine (cirrhosis of the liver)
- Smoking 1.4 cigarettes (cancer, heart disease)
- Spending 1 hour in a coal mine (black lung disease)
- Spending 3 hours in a coal mine (accident)
- Living 2 days in New York or Boston in 1979 (air pollution)
- Living 2 months with a smoker (cancer, heart disease)
- Drinking Miami water for 1 year (cancer from chloroform)
- Eating 100 charcoal-broiled steaks (cancer from benzopyrene)
- Eating 40 tablespoons of peanut butter (liver cancer from aflatoxin B)
- Eating 1000 bananas (cancer from radioactive 1 kBED of Potassium-40)
- Travelling 6000 miles (10,000 km) by jet (cancer due to increased background radiation)
However, such risks might be better handled using the related concept of a microlife.
- Decision theory
- Decision analysis
- Ellsberg paradox
- Precautionary principle
- List of unusual units of measurement
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- Kipps, Courtney; Sanjay Sharma; Dan Tunstall Pedoe (2011-01-01). "The incidence of exercise-associated hyponatraemia in the London marathon". British Journal of Sports Medicine 45 (1): 14–19. doi:10.1136/bjsm.2009.059535. Retrieved 2014-06-12.
- Soreide, Kjetil; Christian Lycke Ellingsen; Vibeke Knutson (2007-05). "How Dangerous is BASE Jumping? An Analysis of Adverse Events in 20,850 Jumps From the Kjerag Massif, Norway". The Journal of Trauma: Injury, Infection, and Critical Care 62 (5): 1113–1117. doi:10.1097/01.ta.0000239815.73858.88. ISSN 0022-5282. PMID 17495709. Retrieved 2014-06-12. Check date values in:
- "The World's Tallest Mountain". Earth Observatory. NASA. 2 January 2014.
- Spiegelhalter, David (10 February 2009). "230 miles in a car equates to one micromort: The agony and Ecstasy of risk-taking". The Times (London). Retrieved 19 April 2009.
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- Blastland, Michael; Spiegelhalter, David (2014). The Norm Chronicles: Stories and Numbers About Danger and Death (1 ed.). Basic Books. p. 8. ISBN 9780465085705.
- Howard, R. A. (1989). "Microrisks for Medical Decision Analysis". International Journal of Technology Assessment in Health Care 5 (3): 357–370. doi:10.1017/S026646230000742X. PMID 10295520.
- Russell, Stuart; Norvig, Peter (2009). Artificial Intelligence (3rd ed.). Prentice Hall. p. 616. ISBN 0-13-604259-7.
- Department for Transport GMH, United Kingdom, "TAG Unit 3.4: The Safety Objective", Transport Analysis Guidance—WebTAG http://www.dft.gov.uk/webtag/documents/expert/unit3.4.1.php
- US Department of Transportation, "Treatment of the Economic Value of a Statistical Life in Departmental Analyses—2011 Interim Adjustment", 2011, http://www.dot.gov/policy/transportation-policy/treatment-economic-value-statistical-life
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