However, loss to follow-up of less than 20% of the overall sample is not considered to imply the presence of considerable bias, even when the missing participants are not missing at random.55 Fourth, although we adjusted for a number of confounding factors in our analyses, unmeasured covariates might still have led to confounding bias, including APOE status, other sleep disorders, and medication use. The gene discussed is APOE; the disease is sleep disorder.