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In a variety of contexts, exogeny or exogeneity (from Greek ἔξω éxō 'outside' and -γένεια -géneia 'to produce') is the fact of an action or object originating externally. It contrasts with endogeneity or endogeny, 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 endogenous random variable is correlated with the error term in the econometric model, while an exogenous variable is not.
- 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, are exogenous.
- The dictionary definition of exogeny at Wiktionary