EXAMPLE 10.22

Computing a 95% confidence interval for the slope. Let’s find a 95% confidence interval for the slope β₁. The degrees of freedom are n − 2 = 4, so t* from Table D is 2.776. We compute

= 0.9185 ± 0.6984

The interval is (0.220, 1.617). For each additional millimeter in diameter, the gestational age of the fetus is expected to be 0.220 to 1.617 weeks older.