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In a variety of contexts, exogeny or exogeneity () 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. For example, in the simple supply and demand model, a change in consumer tastes or preferences is unexplained by the model and also leads to endogenous changes in demand that lead to changes in the equilibrium price. Similarly, a change in the consumer's income is given outside the model but affects demand. Put another way, an exogenous change involves an alteration of a variable that is autonomous, i.e., unaffected by the workings of the model. * In linear regression, an exogenous variable is independent of the random error term in the linear model. * 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. * *Exogenous factors in medicine include both pathogens and therapeutics. * *DNA introduced to cells via transfection or viral infection (transduction) is an exogenous factor. * *Carcinogens are exogenous factors. * 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.〔Posner, M.I. (1980), Orienting of attention. ''Quarterly Journal of Experimental Psychology'', 32: 3 – 25.〕 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 of the natural or influenced realm, is exogenous. ==See also== * Endogenous growth theory * Exogenous growth model 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「exogeny」の詳細全文を読む スポンサード リンク
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