To determine where babies are at the highest risk, researchers map the infant journey into four periods—maternal health/ prematurity, maternal care, newborn care and infant health. A reference group whose population has a low mortality rate is selected. For example, researchers may select white women, with at least 13 years of education between the ages of 20-40 and who are privately insured. This population tends to have the best outcomes in pregnancies and infant survival.
The difference in infant mortality between this reference group and the rest of the population is defined as excess mortality. This indicates the number of potentially preventable deaths if we presume that the whole population can achieve the same low infant-mortality rates as the reference group. In Indiana, about 40 percent of excess mortality is in maternal health / prematurity and 40 percent is in infant health.