OLS effect of X squared ond dependent variable

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I have my OLS regression: $y = beta_1 + beta_2 * X_2 + beta_3 * X_3 +beta_4 * (X_3)^2$



Could anybody please explain to me the effect of a change in $X_3$ on the dependent variable?(Is the effect positive or negative). An example would be greatly appreciated.










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    I have my OLS regression: $y = beta_1 + beta_2 * X_2 + beta_3 * X_3 +beta_4 * (X_3)^2$



    Could anybody please explain to me the effect of a change in $X_3$ on the dependent variable?(Is the effect positive or negative). An example would be greatly appreciated.










    share|cite|improve this question









    New contributor




    P.Cay is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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      up vote
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      down vote

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      up vote
      1
      down vote

      favorite











      I have my OLS regression: $y = beta_1 + beta_2 * X_2 + beta_3 * X_3 +beta_4 * (X_3)^2$



      Could anybody please explain to me the effect of a change in $X_3$ on the dependent variable?(Is the effect positive or negative). An example would be greatly appreciated.










      share|cite|improve this question









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      I have my OLS regression: $y = beta_1 + beta_2 * X_2 + beta_3 * X_3 +beta_4 * (X_3)^2$



      Could anybody please explain to me the effect of a change in $X_3$ on the dependent variable?(Is the effect positive or negative). An example would be greatly appreciated.







      regression mathematical-statistics multiple-regression least-squares marginal-effect






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      edited 19 mins ago









      Ferdi

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          3 Answers
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          As @Tomas already explained greatly in his answer you have to drive to $X_3$.



          $$fracpartial ypartial X_3= beta_3 + 2 times beta_4 times X_3$$.



          As you want to now whether the derivative is positive you face the inquality:



          $$0>beta_3 + 2 times beta_4 times X_3$$.



          Depending on $X_3$ you can change the equation to



          $$frac-beta_32 * beta_4 > X_3$$





          Let us look at an example in which you have real numbers for the Betas:



          When you have the equation:



          $beta_1 = 5$



          $beta_2 = 3$



          $beta_3 = 4$



          $beta_4 = 2$



          $y = 5 + 3 * X_2 + 4 * X_3 + 2 * (X_3)^2$



          and $X_3$ will have a positive effect when:



          $$frac-42 * 2 > X_3$$



          which is simplified:



          $$1 > X_3$$




          Note that the "change in the conditional mean of outcome y when regressors change by one unit" is also called marginal effect. You might look at the tag description and question tagged with this tag to get a broader understanding. In your case you want to know whether the marginal effect of $X_3$ is positive (or negative).






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            up vote
            1
            down vote













            You just take the first derivative of the function with respect to $X_3$:
            $$fracpartial ypartial X_3= beta_3 + 2 times beta_4 times X_3$$
            You may see that the effect of changing $X_3$ on $y$ is not constant but depends on the observed value of $X_3$ (for some, say $i$-th observation).
            Also, ceteris paribus (other things fixed) interpretation holds only with respect to $X_2$, but you cannot change $X_3^2$ while holding $X_3$ fixed.






            share|cite|improve this answer





























              up vote
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              down vote













              The effect that a change in $X_3$ will have on the outcome depend on the coefficients of $beta_3$ and $beta_4$. If both $beta_3$ and $beta_4$ are positive, then any increase in $X_3$ will cause $Y$ to increase. If both $beta_3$ and $beta_4$ are negative, then the an increse in $X_3$ leads to a decrease in $Y$. (Granted, all this is given that $X_3$ is increased without changing the values of $X_2$.)



              If the signs of $beta_3$ and $beta_4$ differ, then the net effect of an increase of $X_3$ on $Y$ will depend on the relative magnitude of $beta_3$ and $beta_4$, as well as the increase in $X_3$.






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                3 Answers
                3






                active

                oldest

                votes








                3 Answers
                3






                active

                oldest

                votes









                active

                oldest

                votes






                active

                oldest

                votes








                up vote
                1
                down vote



                accepted










                As @Tomas already explained greatly in his answer you have to drive to $X_3$.



                $$fracpartial ypartial X_3= beta_3 + 2 times beta_4 times X_3$$.



                As you want to now whether the derivative is positive you face the inquality:



                $$0>beta_3 + 2 times beta_4 times X_3$$.



                Depending on $X_3$ you can change the equation to



                $$frac-beta_32 * beta_4 > X_3$$





                Let us look at an example in which you have real numbers for the Betas:



                When you have the equation:



                $beta_1 = 5$



                $beta_2 = 3$



                $beta_3 = 4$



                $beta_4 = 2$



                $y = 5 + 3 * X_2 + 4 * X_3 + 2 * (X_3)^2$



                and $X_3$ will have a positive effect when:



                $$frac-42 * 2 > X_3$$



                which is simplified:



                $$1 > X_3$$




                Note that the "change in the conditional mean of outcome y when regressors change by one unit" is also called marginal effect. You might look at the tag description and question tagged with this tag to get a broader understanding. In your case you want to know whether the marginal effect of $X_3$ is positive (or negative).






                share|cite|improve this answer
























                  up vote
                  1
                  down vote



                  accepted










                  As @Tomas already explained greatly in his answer you have to drive to $X_3$.



                  $$fracpartial ypartial X_3= beta_3 + 2 times beta_4 times X_3$$.



                  As you want to now whether the derivative is positive you face the inquality:



                  $$0>beta_3 + 2 times beta_4 times X_3$$.



                  Depending on $X_3$ you can change the equation to



                  $$frac-beta_32 * beta_4 > X_3$$





                  Let us look at an example in which you have real numbers for the Betas:



                  When you have the equation:



                  $beta_1 = 5$



                  $beta_2 = 3$



                  $beta_3 = 4$



                  $beta_4 = 2$



                  $y = 5 + 3 * X_2 + 4 * X_3 + 2 * (X_3)^2$



                  and $X_3$ will have a positive effect when:



                  $$frac-42 * 2 > X_3$$



                  which is simplified:



                  $$1 > X_3$$




                  Note that the "change in the conditional mean of outcome y when regressors change by one unit" is also called marginal effect. You might look at the tag description and question tagged with this tag to get a broader understanding. In your case you want to know whether the marginal effect of $X_3$ is positive (or negative).






                  share|cite|improve this answer






















                    up vote
                    1
                    down vote



                    accepted







                    up vote
                    1
                    down vote



                    accepted






                    As @Tomas already explained greatly in his answer you have to drive to $X_3$.



                    $$fracpartial ypartial X_3= beta_3 + 2 times beta_4 times X_3$$.



                    As you want to now whether the derivative is positive you face the inquality:



                    $$0>beta_3 + 2 times beta_4 times X_3$$.



                    Depending on $X_3$ you can change the equation to



                    $$frac-beta_32 * beta_4 > X_3$$





                    Let us look at an example in which you have real numbers for the Betas:



                    When you have the equation:



                    $beta_1 = 5$



                    $beta_2 = 3$



                    $beta_3 = 4$



                    $beta_4 = 2$



                    $y = 5 + 3 * X_2 + 4 * X_3 + 2 * (X_3)^2$



                    and $X_3$ will have a positive effect when:



                    $$frac-42 * 2 > X_3$$



                    which is simplified:



                    $$1 > X_3$$




                    Note that the "change in the conditional mean of outcome y when regressors change by one unit" is also called marginal effect. You might look at the tag description and question tagged with this tag to get a broader understanding. In your case you want to know whether the marginal effect of $X_3$ is positive (or negative).






                    share|cite|improve this answer












                    As @Tomas already explained greatly in his answer you have to drive to $X_3$.



                    $$fracpartial ypartial X_3= beta_3 + 2 times beta_4 times X_3$$.



                    As you want to now whether the derivative is positive you face the inquality:



                    $$0>beta_3 + 2 times beta_4 times X_3$$.



                    Depending on $X_3$ you can change the equation to



                    $$frac-beta_32 * beta_4 > X_3$$





                    Let us look at an example in which you have real numbers for the Betas:



                    When you have the equation:



                    $beta_1 = 5$



                    $beta_2 = 3$



                    $beta_3 = 4$



                    $beta_4 = 2$



                    $y = 5 + 3 * X_2 + 4 * X_3 + 2 * (X_3)^2$



                    and $X_3$ will have a positive effect when:



                    $$frac-42 * 2 > X_3$$



                    which is simplified:



                    $$1 > X_3$$




                    Note that the "change in the conditional mean of outcome y when regressors change by one unit" is also called marginal effect. You might look at the tag description and question tagged with this tag to get a broader understanding. In your case you want to know whether the marginal effect of $X_3$ is positive (or negative).







                    share|cite|improve this answer












                    share|cite|improve this answer



                    share|cite|improve this answer










                    answered 20 mins ago









                    Ferdi

                    3,69042152




                    3,69042152






















                        up vote
                        1
                        down vote













                        You just take the first derivative of the function with respect to $X_3$:
                        $$fracpartial ypartial X_3= beta_3 + 2 times beta_4 times X_3$$
                        You may see that the effect of changing $X_3$ on $y$ is not constant but depends on the observed value of $X_3$ (for some, say $i$-th observation).
                        Also, ceteris paribus (other things fixed) interpretation holds only with respect to $X_2$, but you cannot change $X_3^2$ while holding $X_3$ fixed.






                        share|cite|improve this answer


























                          up vote
                          1
                          down vote













                          You just take the first derivative of the function with respect to $X_3$:
                          $$fracpartial ypartial X_3= beta_3 + 2 times beta_4 times X_3$$
                          You may see that the effect of changing $X_3$ on $y$ is not constant but depends on the observed value of $X_3$ (for some, say $i$-th observation).
                          Also, ceteris paribus (other things fixed) interpretation holds only with respect to $X_2$, but you cannot change $X_3^2$ while holding $X_3$ fixed.






                          share|cite|improve this answer
























                            up vote
                            1
                            down vote










                            up vote
                            1
                            down vote









                            You just take the first derivative of the function with respect to $X_3$:
                            $$fracpartial ypartial X_3= beta_3 + 2 times beta_4 times X_3$$
                            You may see that the effect of changing $X_3$ on $y$ is not constant but depends on the observed value of $X_3$ (for some, say $i$-th observation).
                            Also, ceteris paribus (other things fixed) interpretation holds only with respect to $X_2$, but you cannot change $X_3^2$ while holding $X_3$ fixed.






                            share|cite|improve this answer














                            You just take the first derivative of the function with respect to $X_3$:
                            $$fracpartial ypartial X_3= beta_3 + 2 times beta_4 times X_3$$
                            You may see that the effect of changing $X_3$ on $y$ is not constant but depends on the observed value of $X_3$ (for some, say $i$-th observation).
                            Also, ceteris paribus (other things fixed) interpretation holds only with respect to $X_2$, but you cannot change $X_3^2$ while holding $X_3$ fixed.







                            share|cite|improve this answer














                            share|cite|improve this answer



                            share|cite|improve this answer








                            edited 30 mins ago

























                            answered 36 mins ago









                            Tomas

                            1086




                            1086




















                                up vote
                                0
                                down vote













                                The effect that a change in $X_3$ will have on the outcome depend on the coefficients of $beta_3$ and $beta_4$. If both $beta_3$ and $beta_4$ are positive, then any increase in $X_3$ will cause $Y$ to increase. If both $beta_3$ and $beta_4$ are negative, then the an increse in $X_3$ leads to a decrease in $Y$. (Granted, all this is given that $X_3$ is increased without changing the values of $X_2$.)



                                If the signs of $beta_3$ and $beta_4$ differ, then the net effect of an increase of $X_3$ on $Y$ will depend on the relative magnitude of $beta_3$ and $beta_4$, as well as the increase in $X_3$.






                                share|cite|improve this answer
























                                  up vote
                                  0
                                  down vote













                                  The effect that a change in $X_3$ will have on the outcome depend on the coefficients of $beta_3$ and $beta_4$. If both $beta_3$ and $beta_4$ are positive, then any increase in $X_3$ will cause $Y$ to increase. If both $beta_3$ and $beta_4$ are negative, then the an increse in $X_3$ leads to a decrease in $Y$. (Granted, all this is given that $X_3$ is increased without changing the values of $X_2$.)



                                  If the signs of $beta_3$ and $beta_4$ differ, then the net effect of an increase of $X_3$ on $Y$ will depend on the relative magnitude of $beta_3$ and $beta_4$, as well as the increase in $X_3$.






                                  share|cite|improve this answer






















                                    up vote
                                    0
                                    down vote










                                    up vote
                                    0
                                    down vote









                                    The effect that a change in $X_3$ will have on the outcome depend on the coefficients of $beta_3$ and $beta_4$. If both $beta_3$ and $beta_4$ are positive, then any increase in $X_3$ will cause $Y$ to increase. If both $beta_3$ and $beta_4$ are negative, then the an increse in $X_3$ leads to a decrease in $Y$. (Granted, all this is given that $X_3$ is increased without changing the values of $X_2$.)



                                    If the signs of $beta_3$ and $beta_4$ differ, then the net effect of an increase of $X_3$ on $Y$ will depend on the relative magnitude of $beta_3$ and $beta_4$, as well as the increase in $X_3$.






                                    share|cite|improve this answer












                                    The effect that a change in $X_3$ will have on the outcome depend on the coefficients of $beta_3$ and $beta_4$. If both $beta_3$ and $beta_4$ are positive, then any increase in $X_3$ will cause $Y$ to increase. If both $beta_3$ and $beta_4$ are negative, then the an increse in $X_3$ leads to a decrease in $Y$. (Granted, all this is given that $X_3$ is increased without changing the values of $X_2$.)



                                    If the signs of $beta_3$ and $beta_4$ differ, then the net effect of an increase of $X_3$ on $Y$ will depend on the relative magnitude of $beta_3$ and $beta_4$, as well as the increase in $X_3$.







                                    share|cite|improve this answer












                                    share|cite|improve this answer



                                    share|cite|improve this answer










                                    answered 34 mins ago









                                    Phil

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