Assessing the Impact of Different Race-Bridging Algorithms on the Reported Rate of Birth Defects

In Florida prior to 2004, the birth certificate only allowed parents to identify themselves as 1 race. The birth certificate was subsequently revised in 2004, allowing parents to identify with more than 1 race. This inconsistency in data collection methods can greatly impact the results of race-specific time trend analyses. Race-bridging techniques have been developed to reassign multiple race responses to single race categories. This investigation aimed to compare race-specific birth defect rates calculated in 2 ways: (1) the current method: treating those selecting multiple race categories as though they selected Other race, and (2) the bridged method: attempting to classify those selecting multiple categories into the category they would have selected if they could only pick 1 race.

Data from the Florida Office of Vital Statistics and the Florida Birth Defects Registry were used to examine rates of selected birth defects by race among births to non-Hispanic mothers from 2005 to 2014. Rates of selected birth defects were calculated and compared for the following race groups: white, black, American Indian/Alaska Native (AIAN), and Asian/Pacific Islander (API) using the following 6 bridging methods: (1) no bridging method, (2) largest group, whole allocation, (3) smallest group, whole allocation, (4) largest group other than white, (5) equal fractions, fractional allocation, and (6) reported fractions, fractional allocation.

The differences in birth defect rates comparing the current method to the recalculated bridged-race population depends on the bridging method used. Using largest group, whole-allocation, the total population of white, black, and API races increased, whereas the total number of AIAN remained unaffected. Using the smallest group or largest group other than white, whole-allocation, the total population of black, API, and AIAN increased, resulting in decreased birth defect rates. Lastly, using equal fractions or reported fractions, fractional allocation we found an increase in the live birth count for each race and a corresponding decrease in birth defect rates.

Race-bridging techniques may be useful when reviewing race-specific rates over time, or to account for the lack of comparability of race/ethnic classification in birth defect studies, particularly national studies combining data from different states. However, determining the best race-bridging technique warrants further investigation on larger populations and on other health outcomes.