a spatial or temporal distribution in which individual events tend to occur closer together than expected under the null hypothesis of complete independence or randomness —synonym contagious distribution, aggregated distribution, clustered distribution —note 1. the condition of exhibiting a contagious distribution has been termed overdispersion, i.e., hyperdispersion (larger variance or dispersion than expected under complete randomness) —see dispersion —note 2. the condition in which the distribution is more regular or uniform than expected under complete randomness has been termed underdispersion, i.e., hypodispersion This definition last updated 07/28/2008