Statistical considerations for medication adherence research.

We discourage dichotomizing adherence data as it results in low power. The negative binomial model offers advantages in modeling adherence data, as it avoids the problematic use of a ratio in regression models. The ordinal logistic regression is robust to distributional assumptions with greater power, but naivete to treatment should be adjusted to reserve type I error rate. We also provide a recommendation for defining the observation window in calculating PDC.