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2. Suppose we are given data on n observations (zi, y), î i, . . . , n, and we have a linear model, so that E (Y,) = Ao +Ari. Let A = SXY/Sxx and A,-F-Ax be the least-square estimates given in lecture. (a) Show that E(SXY)-ASxx and E(y)-Ao +AT. (b) Use (a) to show that E (A)-A and E(A)-A- In other words, these are unbiased estimators (c) The fitted values Yī = β0+812 i are used as estimates of E (Y), and the residuals ei-x-Yǐ are used as surrogates for the unobservable errors ε¡ = Yi-E(X). By assumption, E (ei-0. Show that the residuals satisfy a similar property, namely, ei 0. i=1

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