Testing the association between blood type and COVID-19 infection, intubation, and death

Michael Zietz; Nicholas P. Tatonetti

First, we evaluated associations between risk factors and blood groups using logistic regressions of risk factors on blood groups. Second, we verified that risk factors are collectively predictive of COVID-19 outcomes by comparing the fit of a logistic regression model using risk factors to a null model, using only an intercept term. Third, we tested whether blood groups provide additional information on outcomes beyond risk factors by comparing the deviances of a full model (outcome ~ blood group + risk factors) to a nested model using only risk factors (outcome ~ risk factors). Fourth, we tested whether the effects of blood groups are modulated by risk factors by comparing logistic regression coefficients for blood groups between nested (outcome ~ blood group) and full (outcome ~ blood group + risk factors) logistic regression models. In this comparison, the magnitude of blood group coefficients going to zero when risk factors are added would be evidence that outcome is conditionally independent of blood group given risk factors.