Incidentally, applying the F test the reader should verify that the R2 values given in the preceding tables are all statistically significantly different from zero.
We noted earlier that the OLS estimators and their standard errors are sensitive to small changes in the data. In exercise 10.32 the reader is asked to rerun the regression of Y on all the six X variables but drop the last data observations,that is, run the regression for the period 1947–1961. You will see how the regression results change by dropping just a single year’sobservations.
Now that we have established that we have the multicollinearity problem, what “remedial” actions can we take? Let us reconsider our original model.
First of all, we could express GNP not in nominal terms, but in real terms, which we can do by dividing nominal GNP by the implicit price deflator.
Second, since noninstitutional population over 14 years of age grows over time because of natural population growth, it will be highly correlated with time, the variable X6 in our model. Therefore, instead of keeping both these variables, we will keep the variable X5 and drop X6. Third, there is no compelling reason to include X3, the number of people unemployed; perhaps the unemployment rate would have been a better measure of labor market conditions.
But we have no data on the latter. So, we will drop the variable X3.
Making these changes, we obtain the following regression results (RGNP = real GNP)