Incidence of adverse events. Hazard and incidence rate ratios obtained by Cox regression and negative binomial regression, respectively, with and without adjustment for time treated with hydroxyurea. The bars and point estimates for the CIs correspond to the crude incidence rate ratios. ∗The adjusted result is from a Poisson mixed-effects regression model as the negative binomial counterpart did not converge or had a non-positive variance estimated for the random intercept. †Hazard ratio is computed for this binary outcome with hydroxyurea as a time-varying covariate. Incidence rate ratios are computed for other outcomes. ‡ No convergence (no event in the zinc group).