Definition of overdispersion in US English:

overdispersion

noun

Statistics
  • 1Greater 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.

  • 2Greater separateness or regularity of distribution than would be predicted to arise randomly.

Origin

1930s. From over- + dispersion. Compare under-dispersion.

Pronunciation

overdispersion

/ˌəʊvədɪˈspəːʃn/