The March of Dimes index of racial/ethnic disparity ("disparity index") in preterm birth provides a measure of the differences, or disparities, in preterm birth rates across racial/ethnic groups within a geographic area. The index was developed by the March of Dimes Perinatal Data Center and is calculated for each U.S. state with adequate numbers, the District of Columbia and the total United States.
To calculate the disparity index, the lowest preterm birth rate among the displayed racial/ethnic groups is identified for a geographic area and used as the comparison rate. The percent difference between the preterm birth rate and the comparison rate is calculated for each of the remaining racial/ethnic groups. The percent differences are then averaged to produce the index number, displayed as an integer. The disparity index number can be 0 or greater, with 0 representing no difference between groups. The unrounded index number for each geographic area is ranked against all other geographic areas, with the rank of #1 indicating the least disparity.
The report card also provides the percent difference between the racial/ethnic group with the highest preterm birth rate compared to the combined preterm birth rate among women in all other racial/ethnic groups in the state or jurisdiction. This percent difference is calculated using only the racial/ethnic groups displayed on the state- or jurisdiction-specific report card. This difference is calculated for each U.S. state with adequate numbers and the District of Columbia.