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In a variety of contexts, exogeny or exogeneity (from Greek exo, meaning 'outside', and gignomai, meaning 'to produce') is the fact of an action or object originating externally. It contrasts with endogeny or endogeneity, the fact of being influenced within a system.
- In an economic model, an exogenous change is one that comes from outside the model and is unexplained by the model.
- In econometrics, an exogenous variable is assumed to be fixed in repeated sampling, which means it is a nonstochastic variable. An implication of this assumption is that the error term in the econometric model is independent of the exogenous variable.
- In biology, an exogenous contrast agent in medical imaging for example, is a liquid injected into the patient intravenously that enhances visibility of a pathology, such as a tumor. An exogenous factor is any material that is present and active in an individual organism or living cell but that originated outside that organism, as opposed to an endogenous factor.
- In geography, exogenous processes all take place outside the Earth and all the other planets. Weathering, erosion, transportation and sedimentation are the main exogenous processes.
- In attentional psychology, exogenous stimuli are external stimuli without conscious intention. An example of this is attention drawn to a flashing light in the periphery of vision.
- In ludology, the study of games, an exogenous item is anything outside the game itself. Therefore, an item in a massively multiplayer online game would have exogenous value if people were buying it with real world money rather than in-game currency (though its in-game cost would be endogenous).
- In materials science, an exogenous property of a substance is derived from outside or external influences, such as a nano-doped material.
- In philosophy, the origins of existence of self, or the identity of self, emanating from, or sustaining, outside the natural or influenced realm, is exogenous.
- The dictionary definition of exogeny at Wiktionary