Exogenous and endogenous variables: Difference between revisions

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In an economic model, an exogenous variable is one that 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}

In contrast, an endogenous variable is a variable whose value is determined by the model. An endogenous change is a change in an endogenous variable in response to an exogenous change that is imposed upon the model.^[1]^{: p. 8}^[1]^{: p. 8}

Examples

In the simple supply and demand model, a change in consumer tastes is unexplained by the model and imposes an exogenous change in demand that leads to a change in the endogenous equilibrium price and the endogenous equilibrium quantity transacted. Here the exogenous variable is a parameter conveying consumer tastes. Similarly, a change in the consumer's income is exogenously given, outside the model, and appears in the model as an exogenous change in demand.^[1]^{: p. 10}

In the LM model of interest rate determination, the supply of and demand for money determine the interest rate contingent on the level of the money supply, so the money supply is an exogenous variable and the interest rate is an endogenous variable.

In a model of firm behavior with competitive input markets, the prices of inputs are exogenously given, and the amounts of the inputs to use are endogenous.^[2]^{: p. 202}

Sub-models and models

An economic variable can be exogenous in some models and endogenous in others. In particular this can happen when one model also serves as a component of a broader model. For example, the IS model of only the goods market derives the market-clearing (and thus endogenous) level of output depending on the exogenously imposed level of interest rates, since interest rates affect the physical investment component of the demand for goods. In contrast, the LM model of only the money market takes income (which identically equals output) as exogenously given and affecting money demand; here equilibrium of money supply and money demand endogenously determines the interest rate. But when the IS model and the LM model are combined to give the IS-LM model, both the interest rate and output are endogenously determined.

Category:Technical terminology

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^ ^a ^b ^c ^d Mankiw, N. Gregory. Macroeconomics, third edition, 1997.
^ ^a ^b Varian, Hal R., Microeconomic Analysis, third edition, 1992.

[Mankiw-1] Mankiw, N. Gregory. Macroeconomics, third edition, 1997.

[Varian-2] Varian, Hal R., Microeconomic Analysis, third edition, 1992.

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-In an [[economics|economic]] [[model (economics)|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 is unexplained by the model and imposes an exogenous change in demand that leads to a change in the [[economic equilibrium|equilibrium]] price. Here the '''exogenous variable''' is a [[parameter]] conveying consumer tastes. Similarly, a change in the consumer's income is given outside the model and affects demand exogenously. Put another way, an exogenous change involves an alteration of a variable that is autonomous, i.e., unaffected by the workings of the [[model (economics)|model]].
+In an [[economics|economic]] [[model (economics)|model]], an '''exogenous variable''' is one that is determined outside the model and is imposed on the model, and an '''exogenous change''' is a change in an exogenous variable.<ref name=Mankiw>Mankiw, N. Gregory. ''Macroeconomics'', third edition, 1997.</ref>{{rp|p. 8}}<ref name=Varian>Varian, Hal R., ''Microeconomic Analysis'', third edition, 1992.</ref>{{rp|p. 202}}
-In contrast, an '''endogenous variable''' is one whose value is determined within the model. For example, in the [[liquidity preference]] model, the supply of and demand for [[money]] determine the [[interest rate]], so the interest rate is an endogenous variable.
+In contrast, an '''endogenous variable''' is a variable whose value is determined by the model. An '''endogenous change''' is a change in an endogenous variable in response to an exogenous change that is imposed upon the model.<ref name=Mankiw/>{{rp|p. 8}}<ref name=Mankiw/>{{rp|p. 8}}
+==Examples==
+In the simple [[supply and demand]] model, a change in consumer tastes is unexplained by the model and imposes an exogenous change in demand that leads to a change in the endogenous [[economic equilibrium|equilibrium]] price and the endogenous equilibrium quantity transacted. Here the exogenous variable is a [[parameter]] conveying consumer tastes. Similarly, a change in the consumer's income is exogenously given, outside the model, and appears in the model as an exogenous change in demand.<ref name=Mankiw/>{{rp|p. 10}}
+In the [[IS–LM model|LM model]] of interest rate determination, the supply of and demand for [[money]] determine the [[interest rate]] contingent on the level of the money supply, so the [[money supply]] is an exogenous variable and the interest rate is an endogenous variable.
+In a model of [[firm behavior]] with competitive input markets, the prices of [[input (economics)|inputs]] are exogenously given, and the amounts of the inputs to use are endogenous.<ref name=Varian/>{{rp|p. 202}}
 ==Sub-models and models==
-An economic variable can be exogenous in some models and endogenous in others. In particular this can happen when one model also serves as a component of a broader model. For example, the [[IS-LM|IS]] model of only the goods market derives the market-clearing (and thus endogenous) level of [[output (economics)|output]] depending on the exogenously imposed level of [[interest rate]]s, since interest rates affect the [[physical investment]] component of the demand for goods. In contrast, the [[IS-LM|LM]] model of only the money market takes income (which [[identity (mathematics)|identically]] equals output) as exogenously given and affecting [[money demand]]; here equilibrium of money supply and money demand endogenously determines the interest rate. Moreover, the IS model and the LM model can be combined to give the [[IS-LM model]], in which both the interest rate and output are endogenously determined.
+An economic variable can be exogenous in some models and endogenous in others. In particular this can happen when one model also serves as a component of a broader model. For example, the [[IS-LM|IS]] model of only the goods market derives the market-clearing (and thus endogenous) level of [[output (economics)|output]] depending on the exogenously imposed level of [[interest rate]]s, since interest rates affect the [[physical investment]] component of the demand for goods. In contrast, the [[IS-LM|LM]] model of only the money market takes income (which [[identity (mathematics)|identically]] equals output) as exogenously given and affecting [[money demand]]; here equilibrium of money supply and money demand endogenously determines the interest rate. But when the IS model and the LM model are combined to give the [[IS-LM model]], both the interest rate and output are endogenously determined.
 [[:Category:Technical terminology]]