The contrast statement uses the comma to join together what would have been two separate one degree of freedom tests into a single two degree of freedom test that tests the null hypothesis above. Since Chow test is mostly used in time series, SAS has included it with proc autoreg.
The null hypothesis to be tested is. We also create age1ht that is age1 times height , and age2ht that is age2 times height.
The second contrast compares the regression coefficients of the young vs. The Chow test indicates that there is a structural difference for male and female students. We can now use age1 age2 height , age1ht and age2ht as predictors in the regression equation in proc reg below. It is used mostly in time-series models.
We can do the exact same analysis in proc reg by coding age1 and age2 like the coding shown in the contrast statements above We will create age1 that will be:.
Indeed, for the comparison of Middle age vs. If the estimation is an instrumental variables estimation with matrix of instruments , then the following regression is performed:. Previous Page Next Page. In this example, we use proc freq to identify the position for the breakpoint and we then have to sort the data accordingly. Chow Tests The Chow test is used to test for break points or structural changes in a model.
The significance tests in proc reg below for age1ht and age2ht will correspond to the contrast statements we used in proc glm above. This test can be derived from the Chow test by noting that the when and by adjusting the degrees of freedom appropriately.
The parameter estimates coefficients for the young, middle age, and senior citizens are shown below. The problem is posed as a partitioning of the data into two parts of size and. The first contrast compares the regression coefficients of the middle aged vs.
Instead of using a test statement, the contrast statement is used to test the null hypothesis. In this instance, the predictive Chow test can be used.