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In an economic model, an exogenous variable is one whose measure is determined outside the model and is imposed on the model, and an exogenous change is a change in an exogenous variable. [1]: p. 8 [2]: p. 202 [3]: p. 8 In contrast, an endogenous variable is a variable whose measure is determined by the model. An endogenous change is a change ...
Exogeneity is articulated in such a way that a variable or variables is exogenous for parameter . Even if a variable is exogenous for parameter α {\displaystyle \alpha } , it might be endogenous for parameter β {\displaystyle \beta } .
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 and endogenous variables in economic models; Endogenous growth theory in economics; Endogenous preferences in economics; Endogenous money; In context of ...
This is a weaker restriction than strict exogeneity, which requires the variable to be uncorrelated with past, present, and future shocks. A common example of a predetermined variable is consumption in models with credit constraints and rational expectations. Here, consumption is predetermined but not strictly exogenous.
In the first stage, each explanatory variable that is an endogenous covariate in the equation of interest is regressed on all of the exogenous variables in the model, including both exogenous covariates in the equation of interest and the excluded instruments. The predicted values from these regressions are obtained:
These variables are termed exogenous; the remainder, determined by the model, is called endogenous. The choice of which variables are to be exogenous is called the model closure, and may give rise to controversy. For example, some modelers hold employment and the trade balance fixed; others allow these to vary. Variables defining technology ...
The AK model, which is the simplest endogenous model, gives a constant-savings rate of endogenous growth and assumes a constant, exogenous, saving rate. It models technological progress with a single parameter (usually A).