15.5 Estimating the effect of smoking Refer to the previous exercise. For these data, MINITAB reports:

Point estimate for η1 − η2 is −2.00 95.9 Percent CI for η1 − η2 is (−3.30,−0.70)

W = 31.0 Test of η1 = η2 vs η1 • η2 is significant at 0.006 Explain how to interpret the reported

(a) point estimate and

(b) confidence interval.