Selection due to survival or attrition may bias estimates of racial disparities in health, but few studies quantify the likely magnitude of such bias. In a large national cohort with moderate loss to follow-up, Drs. Leann Long, George Howard, Dustin Long, and Suzanne Judd from the department of biostatistics at the University of Alabama at Birmingham School of Public Health collaborated with other researchers to contrast racial differences in two stroke risk factors, incident hypertension and incident left ventricular hypertrophy estimated by complete case analyses, inverse probability of attrition weighting, and the Survivor Average Causal Effect.
The team utilized data on 12,497 black and 17,660 white participants enrolled from 2003 through 2007 and collected incident risk factor data approximately 10 years after baseline. At follow-up, 21.0 percent of whites and 23.0 percent of blacks had died; additionally 22.0 percent of whites and 28.4 percent of blacks had withdrawn. Individual probabilities of completing the follow-up visit were estimated using baseline demographic and health characteristics.
Adjusted risk ratio estimates of racial disparities from complete case analyses in both incident hypertension (1.11 [95 percent CI: 1.02, 1.21]) and incident left ventricular hypertrophy (1.02 [95 percent CI: 0.84, 1.24]) were virtually identical to estimates from inverse probability of attrition weighting and Survivor Average Causal Effect.
Despite racial differences in mortality and attrition, the authors found little evidence of selection bias in the estimation of racial differences for these incident risk factors.