You have been asked to consider a regression model which relates the behaviour of three time series, Y;,Xt, Zt where t = 1, 2, . . . ,T. The proposed model is as follows: Y1; = 50 'l' lXt 'l' 52X? 'l' i63Zt + 'U: Before relying on the results of an ordinary least squares (OLS) estimate of the model above identify two issues you might investigate. For each of the two issues you should: (i) Define the issue in the context of the model. (ii) Identify what issues this might cause when relying on the results of the OLS regres- sion. (iii) Explain how you would test for the presence of the issue. (iv) Suggest how you might solve the problem in order to obtain useful estimates of the model [25 MARKS]