overdispersionn.

Brit.

/ˌəʊvədᵻˈspəːʃn/, U.S.

/ˈˌoʊvərdəˈspərʃ(ə)n/,

/ˈˌoʊvərdəˈspərʒ(ə)n/

Origin: Formed within English, by derivation. Etymons: over- prefix, dispersion n.

Etymology: < over- prefix + dispersion n. Compare under-dispersion n.

Chiefly Statistics.

1. Greater variance in a set of observations than would be expected on the assumption of independence and homogeneity (which underlies e.g. binomial and Poisson distribution); greater unevenness in the distribution of individuals, events, etc., than would be the case if each instance were independent of the rest; clustering, aggregation.

ΘΚΠ

the world > life > biology > balance of nature > distribution > [noun]

cosmopolitanism1870

endemicity1886

endemism1886

bipolarity1896

radiation1898

zonation1898

frequency1913

provincialism1929

overdispersion1930

under-dispersion1935

provinciality1952

1930 L. G. Romell in Ecology 11 593 Making a series of analyses, using areas of different size.., one will find the dispersion to change from a strong overdispersion, with small areas, to a more nearly normal dispersion, with larger areas.

1936 Jrnl. Ecol. 24 234 If in a set of counts of numbers of individuals per sample area the relative variance is greater than unity, this indicates that the dispersion is greater than would be expected on the assumption of random (Poisson) distribution... [This] first condition, over-dispersion, implies that individuals are scattered less evenly..than would be expected.

1961 Amer. Naturalist 95 42 Where the data do not fit the Poisson distribution, the aberrations are overdispersed, that is, there are too many cells containing multiple aberrations. There is also a tendency toward such overdispersion in the rest of the data.

1989 P. McCullagh & J. A. Nelder Generalized Linear Models (ed. 2) iv. 124 By the term ‘over-dispersion’ we mean that the variance of the response Y exceeds the nominal variance—in this case the nominal binomial variance, mπ(1 - π).

1998 Admin. Sci. Q. 43 856 Poisson models can produce biased results when count data show a variance that is much larger than the mean, a situation termed overdispersion.

2. Greater separateness or regularity of distribution than would be predicted to arise randomly; = overdispersal n.This is opposed in meaning to the statistical use defined at sense 1, and corresponds to the ordinary sense of dispersion (as applied to the spatial location of objects: cf. dispersion n. 1) rather than to the technical sense (as applied to the statistical distribution of data: cf. dispersion n. 6).

ΚΠ

1931 Proc. National Acad. Sci. U.S.A. 17 598 Bulbocapnine produced a marked improvement in the case of a man already suffering from over-dispersion of certain of the brain colloids... Bulbocapnine must be an agglomerating agent in man.

1938 Jrnl. Ecol. 26 456 (note) Ashby's interpretation appears to be more logical... Thus over-dispersion means that the individuals are spaced further apart while under-dispersion indicates aggregation of the individuals.

1973 Jrnl. Animal Ecol. 42 815 Territoriality is common in ants and is a causative factor of overdispersion in many species.

1990 Behavioural Ecol. 1 38/2 The expected ratio of variance to mean equals 1. Clumping and overdispersion would give values greater than or less than this, respectively.

This entry has been updated (OED Third Edition, December 2004; most recently modified version published online March 2022).

单词	overdispersion
释义	overdispersionn. Brit. /ˌəʊvədᵻˈspəːʃn/, U.S. /ˈˌoʊvərdəˈspərʃ(ə)n/, /ˈˌoʊvərdəˈspərʒ(ə)n/ Origin: Formed within English, by derivation. Etymons: over- prefix, dispersion n. Etymology: < over- prefix + dispersion n. Compare under-dispersion n. Chiefly Statistics. 1. Greater variance in a set of observations than would be expected on the assumption of independence and homogeneity (which underlies e.g. binomial and Poisson distribution); greater unevenness in the distribution of individuals, events, etc., than would be the case if each instance were independent of the rest; clustering, aggregation. ΘΚΠ the world > life > biology > balance of nature > distribution > [noun] cosmopolitanism1870 endemicity1886 endemism1886 bipolarity1896 radiation1898 zonation1898 frequency1913 provincialism1929 overdispersion1930 under-dispersion1935 provinciality1952 1930 L. G. Romell in Ecology 11 593 Making a series of analyses, using areas of different size.., one will find the dispersion to change from a strong overdispersion, with small areas, to a more nearly normal dispersion, with larger areas. 1936 Jrnl. Ecol. 24 234 If in a set of counts of numbers of individuals per sample area the relative variance is greater than unity, this indicates that the dispersion is greater than would be expected on the assumption of random (Poisson) distribution... [This] first condition, over-dispersion, implies that individuals are scattered less evenly..than would be expected. 1961 Amer. Naturalist 95 42 Where the data do not fit the Poisson distribution, the aberrations are overdispersed, that is, there are too many cells containing multiple aberrations. There is also a tendency toward such overdispersion in the rest of the data. 1989 P. McCullagh & J. A. Nelder Generalized Linear Models (ed. 2) iv. 124 By the term ‘over-dispersion’ we mean that the variance of the response Y exceeds the nominal variance—in this case the nominal binomial variance, mπ(1 - π). 1998 Admin. Sci. Q. 43 856 Poisson models can produce biased results when count data show a variance that is much larger than the mean, a situation termed overdispersion. 2. Greater separateness or regularity of distribution than would be predicted to arise randomly; = overdispersal n.This is opposed in meaning to the statistical use defined at sense 1, and corresponds to the ordinary sense of dispersion (as applied to the spatial location of objects: cf. dispersion n. 1) rather than to the technical sense (as applied to the statistical distribution of data: cf. dispersion n. 6). ΚΠ 1931 Proc. National Acad. Sci. U.S.A. 17 598 Bulbocapnine produced a marked improvement in the case of a man already suffering from over-dispersion of certain of the brain colloids... Bulbocapnine must be an agglomerating agent in man. 1938 Jrnl. Ecol. 26 456 (note) Ashby's interpretation appears to be more logical... Thus over-dispersion means that the individuals are spaced further apart while under-dispersion indicates aggregation of the individuals. 1973 Jrnl. Animal Ecol. 42 815 Territoriality is common in ants and is a causative factor of overdispersion in many species. 1990 Behavioural Ecol. 1 38/2 The expected ratio of variance to mean equals 1. Clumping and overdispersion would give values greater than or less than this, respectively. This entry has been updated (OED Third Edition, December 2004; most recently modified version published online March 2022). < n.1930
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