heterogeneity

Heterogeneity is the quality of being diverse in components or characteristics within a system, population, or material. It denotes variation rather than uniformity and can result from genetic, environmental, developmental, or random factors that differ across space and time.

In statistics, heterogeneity refers to differences in study design, populations, interventions, or outcomes across studies. It is commonly quantified with metrics such as I-squared and Cochran’s Q. When substantial, random-effects models and subgroup analyses help generalize findings and identify sources of variability.

In materials science, heterogeneity describes nonuniform microstructure or composition—such as phase distribution, grain size, or porosity—that affects properties like strength, conductivity, or durability.

In biology and medicine, it includes genetic or clonal diversity within populations or tumors, influencing disease progression and treatment response. Tumor heterogeneity, in particular, challenges therapies and motivates approaches such as multi-region sequencing.

In ecology and geography, spatial or environmental heterogeneity describes nonuniform habitats or conditions that shape species distributions, ecosystem processes, and resilience.

Social sciences recognize heterogeneity in attitudes, behaviors, and sociodemographic characteristics, affecting sampling, inference, and policy evaluation.