For the proportional hazards model ln[(????)] = ln[0(????)] + ????1????1 + ????2????2, suppose that ????1 = 0.87,

For the proportional hazards model ln[ℎ(????)] = ln[ℎ0(????)] + ????1????1 + ????2????2, suppose that ˆ????1 = 0.87, ????????(ˆ????1) = 0.91, ˆ????2 = −1.57, and ????????(ˆ????2) = 0.69.

(a) Test ????0 ∶ ????1 = 0 at the ???? = 0.05 level. Be sure to compute the ????-value for this test.

(b) Test ????0 ∶ ????2 = 0 at the ???? = 0.05 level. Be sure to compute the ????-value for this test.

(c) Based on the hypothesis tests in parts

(a) and

(b) is there sufficient statistical evidence to suggest that both ????1 and ????2 are needed in the model? Explain.