Although the sample size gives a reasonable estimate of variance [57], it limited the use of age, sex, comorbidities such as ADHD [71], interindividual EEG variation due to methylenetetrahydrofolate reductase mutation [72] and time of electroencephalogram collection [73] as covariates in the analysis of study outcomes. The gene discussed is MTHFR; the disease is attention deficit-hyperactivity disorder.