A unit of risk used to compare and assign monetary values to risky activities. Symbol, μmt. One micromort is one chance in a million (hence the SI prefix “micro-”) of dying on the spot. A skydive, for example, is rated at 7 to 10 micromorts.
The term was coined by Ronald A. Howard in 1979. It is meant to be used only for activities where the risk is small.
To simplify the use of the small-risk life value and to emphasize the necessity that it be used only when the risk to life is small, we find it useful to define a unit for small risks in life. We shall use the term “micromort” to mean a one in a million chance of death, with symbol μmt.
Ronald A. Howard.
On making life and death decisions.
Richard C. Schwing and Walter A. Albers, Jr., editors.
Societal Risk Assessment, How Safe Is Safe Enough?
Proceedings of an international symposium held Oct. 8-9, 1979 at the General Motors Research Laboratories, Warren, Mich. and sponsored by the Laboratories.
New York: Plenum Press, 1980.
ISBN 0306405547 9780306405549
Howard (1984) proposes using the value of a micromort**an incremental mortality risk of 10⁻⁶, instead of the value of life. The use of micromorts may be preferred because it avoids the misleading impression that one would sell his or her life for “the value of life.” However, the value of life has become the conventional measure for valuing risks so we adhere to this convention. The value of a micromort is simply 10⁻⁶ times the implicit value of life.
James K Hammitt.
Outcome and Value Uncertainty in Environmental Policy.
Santa Monica, CA: RAND Corporation, 1988.
http://www.rand.org/pubs/papers/P7457. Also available in print form.
Page 166, footnote.
Wikipedia lists micromort values for a number of activities:
Michael Blastland and David Spiegelhalter.
The Norm chronicles: stories and numbers about danger and death.
New York: Basic Books, 2014.
Layla Skinns, Michael Scott and Tony Cox, editors.
Cambridge University Press, 2011.
D. J. Spiegelhalter.
The power of the MicroMort.
BJOG: An International Journal of Obstetrics and Gynecology, vol 121, issue 6, pages 662-663 (May 2014)
Hannah A. D. Keage and Tobias Loetscher.
Estimating everyday risk: Subjective judgments are related to objective risk, mapping of numerical magnitudes and previous experience.
PLOS One, December 5, 2018. doi: https://doi.org/10.1371/journal.pone.0207356
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Last revised: 2 June 2015.