Suppose you are interested in estimating the causal effect of having a Master's degree in Eco- nomics on earnings among individuals who majored in Economics. You have a sample of 1,500 individuals who majored in Economics. Which of the following statements is correct: O A consistent estimate of this causal effect can be obtained by comparing average earnings of sampled individuals with and without a Master's degree in Economics O A consistent estimate of this causal effect can be obtained by regressing earnings on a dummy variable indicating whether or not an individual in the sample has a Master's degree in Economics O A consistent estimate of this causal effect can be obtained by regressing earnings on 1) a dummy variable indicating whether an individual in the sample has a Master's degree in Economics, 2) gender, 3) age, 4) type of occupation, 5) state of residence O None of the above

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1 -1 A = | 2 3 1 1 1 2 2 -1 Ex: 5 : A-1

22. With A as in Exercise 3, find a nonzero vector in Nul A, a nonzero vector in Col A, and a nonzero vector in Row A. 127 Fo