Review the Concepts 7.1 Explain how you would test the null hypothesis that 1=0 in the multiple regression model Yi=0+1X1i+2X2i+ui. Explain how you would test the null hypothesis that 2=0. Explain how you would test the joint hypothesis that 1=0 and 2=0. Why isn't the result of the joint test implied by the results of the first two tests? 7.2 Provide an example of a regression that arguably would have a high value of R2 but would produce biased and inconsistent estimators of a causal effect. Explain why the R2 is likely to be high. Explain why the OLS estimators would be biased and inconsistent. 7.3 What is a control variable, and how does it differ from a variable of interest? Looking at Table 7.1 , for what factors are the control variables controlling? Do coefficients on control variables measure causal effects? Explain