propensities

Propensity (plural propensities) denotes a natural inclination, disposition, or tendency to behave in a particular way or to experience certain outcomes. The term is used widely across disciplines to describe the likelihood of events given background conditions, as well as to characterize habitual dispositions in people or systems. In everyday language propensities describe things such as a propensity for risk-taking or for linguistic fluency. In philosophy and psychology, propensities are discussed as dispositions that tend to produce specific effects under suitable circumstances.

Statistical use centers on the propensity score, defined as the probability that a unit receives a treatment given observed covariates. Propensity scores are used in observational studies to reduce confounding by balancing covariate distributions between treated and untreated groups. Common methods include matching on the propensity score, stratification, inverse probability weighting, and regression adjustment. The concept was introduced by Rosenbaum and Rubin in 1983. While helpful, propensity-based methods rely on the assumption that all confounders are observed and correctly modeled; they do not address unmeasured confounding and require adequate overlap of covariate distributions between groups.

Other uses of the term appear in chemistry and physics, where propensities describe the likelihood of a reaction or process under given conditions, and in a philosophical account of causation, where propensities denote the dispositional tendencies of entities to bring about certain outcomes. Across fields, the idea of propensity emphasizes probabilistic tendency rather than fixed determinism.