Suppose the true regression model is given by (4-8). The result in (4-10) shows that if either P 1.2 is nonzero or 2 is

Suppose the true regression model is given by (4-8). The result in (4-10) shows that if either P_1.2 is nonzero or β₂ is nonzero, then regression of y on X₁ alone produces a biased and inconsistent estimator of β₁. Suppose the objective is to forecast y, not to estimate the parameters. Consider regression of y on X₁ alone to estimate β₁ with b₁ (which is biased). Is the forecast of y computed using X₁b₁ also biased? Assume that E[X₂ | X₁] is a linear function of X₁. Discuss your findings generally. What are the implications for prediction when variables are omitted from a regression?