EXAMPLE 10.16

Umbilical cord diameter and gestational age. Knowing the gestational age (GA) of a fetus is important for biochemical screening tests and planning for successful delivery. Typically GA is calculated as the number of days since the start of the woman’s last menstrual period (LMP). However, for women with irregular periods, GA is difficult to compute, and ultrasound imaging is often used. In the search for helpful ultrasound measurements, a group of Nigerian researchers looked at the relationship between umbilical cord diameter (mm) and gestational age based on LMP (weeks).⁸ Here is a small subset of the data:

The data and the least-squares line are plotted in Figure 10.16. The strong straight-line pattern suggests that we can use linear regression to model the relationship between cord diameter and gestational age.