Age range of the sample is another important consideration. Many EEG and ERP phenotypes show substantial age-related changes, and large variability in age within the sample may inflate twin correlation both in MZ and DZ pairs, leading to an overestimation of the shared environmental influences. Therefore, it can be recommended that age-related trend is removed in regression analyses before entering the data in genetic analyses or, alternatively, age effects should be included in the biometrical model. Of note, a linear regression will likely be insufficient in many cases due to nonlinear shape of age-related trends for many variables such as resting EEG band powers and P3 amplitude.
