EXAMPLE 10.23

Computing a confidence interval for m. Let’s find a 95% confidence interval for the average gestational age when the umbilical cord diameter is 10 millimeters. The estimated mean age is

= 15.1859 + (0.9185)(10)

= 24.371

The standard error is

= 2.021

To find the 95% confidence interval, we compute

= 24.371 ± 5.610

The interval is 18.761 to 29.981 weeks of age. This is a pretty wide interval given gestation lasts for about 40 weeks.