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The J-shaped Probability Distribution

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Up to now, research foresters have lacked an appropriate probability distribution for tree diameter as measured in an uneven-aged stand or forest. A probability distribution--herein called the J-shaped distribution--that should prove applicable to tree diameter and similar variables is derived and described. This distribution belongs to the exponential family, is sometimes called the negative exponential distribution, and has been applied to certain non-forestry problems. The cumulative distribution function is F(x) = 1 - e-rx and the probability density function is f(x) = re-rx where: e is the base for natural logarithms, r > 0 is the one parameter of the distribution, and x ≥ 0 is the independent variable (tree diameter). Expressions are presented for the mean and variance; the conditional distribution, mean, and variance; and the characteristic function. The mean of several variables with a common J-shaped distribution is not distributed the same as the component variables; in other words, the J-shaped distribution is not reproductive. Possibly, this probability distribution will be found applicable to certain other continuous variables commonly used in forestry research.

Document Type: Journal Article

Affiliations: Research Forester, Northeastern Forest Expt. Sta., Forest Service, U. S. Dept. of Agric., Upper Darby, Pa.

Publication date: 1965-12-01

More about this publication?
  • Forest Science is a peer-reviewed journal publishing fundamental and applied research that explores all aspects of natural and social sciences as they apply to the function and management of the forested ecosystems of the world. Topics include silviculture, forest management, biometrics, economics, entomology & pathology, fire & fuels management, forest ecology, genetics & tree improvement, geospatial technologies, harvesting & utilization, landscape ecology, operations research, forest policy, physiology, recreation, social sciences, soils & hydrology, and wildlife management.
    Forest Science is published bimonthly in February, April, June, August, October, and December.

    2015 Impact Factor: 1.702
    Ranking: 16 of 66 in forestry

    Also published by SAF:
    Journal of Forestry
    Other SAF Publications
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