<p>Normative databases are constructed and validated based upon the scientific standards of gaussianity, cross-validation, amplifier matching and peer reviewed publications. Normative databases must use healthy participants who do not have any psychological or physiological pathologies.&nbsp;A clinically normal database is one where individuals are carefully screened for relevant abnormalities using other clinical tools such as psychometric assessment or MRIs.&nbsp;While it may be too expensive and exhaustive to require that all individuals have full MRI, PET, fMRI, complete neuropsychological evaluation, genetic analysis, blood and urine testing, etc., it would be ideal. A second-best option, then, is to get questionnaire information and objective assessments of general health, and social and intellectual functioning.</p><p>The database should represent the mix of ages, gender, ethnicity, socioeconomic status and other demographic factors present in the overall population. “Representative sampling” means a demographically balanced sample of different genders, different ethnic backgrounds, different socio-economic status and different ages. Using a rigorously screened population, deviations represent the difference from “well-functioning” as compared to “average.” Poor screening procedures result in admitting individuals into a normal group who have significant clinical problems. Careful screening of the subjects that comprise a normative database is critical so that representative samples of healthy and otherwise normally functioning individuals are selected and individuals with a history of neurological problems, psychiatric problems, school failure and other deviant behaviors are excluded. It is especially important to get many children sampled in a normative database, because dramatic developmental changes occur in children and adolescents in relatively short time intervals. Where two years difference will not alter the demographics of an adult, it can signify important differences in, say, a 4-year-old and a 6-year-old.&nbsp;</p><p><span style="font-size: 1rem;">It is important for a database to have a large sample size, although ultimately this criterion is less important than careful calibration, elimination of artifact, rigorous standards during data collection and rigorous standards for data analysis and approximation to a Gaussian distribution. To be considered a clinically valid normative database, there must be peer review (published), tests of reliability, tests of statistical validity, cross-validation tests, full disclosure of the inclusion and exclusion criteria, and adequate sample sizes for different age groups.&nbsp;</span></p><p><span style="font-size: 1rem;">Figure xx: Asymmetry in Quantitative EEG Maps (NeuroGuide)<br></span></p><p style="text-align: center;"><span style="font-size: 1rem;"><img src="@@PLUGINFILE@@/asymmetry-z-scored.png" alt="Asymmetry in Quantitative EEG Maps (NeuroGuide)" width="712" height="538" role="presentation" class="img-responsive atto_image_button_text-bottom"><br></span></p><p style="text-align: left;"><span style="font-size: 1rem;">Many normative databases available for clinical use contain the mean values of EEG features (absolute power, relative power, coherence measures, etc.); the “normative” quantification of theta data is the standard deviation of the features relative to the normal population (see John, Prichep, &amp; Easton, 1987). Certain databases provide magnitude (the square root of power), while others provide amplitude (which is power measured in microvolts squared).&nbsp; Relative power represents the percentage of power in any bands compared with the total power in the patient’s EEG (e.g., “relative theta” is the percentage of theta of the combined sum of delta, theta, alpha, and beta). One way to describe relative power is “how the client spends their time.” Other derived measures that have been normed include hemispheric asymmetry for power (which often reflects the power differential between different sites in the brain), coherence (the stability of the phase relationship between electrode sites, and phase (the measure of time delay between activities at two sites). It should be recognized that these measures are not statistically independent, and significant deviations on more than one feature may be representing the same neurophysiological process (i.e. hypercoherence in alpha may also be represented in a global alpha amplitude deviation, due to a contaminated reference).&nbsp; While some normative databases rely on a linked ears reference, the savvy clinician will reference a database that has multiple montage possibility (in the case of contaminated reference). A problem with most of the currently available databases is the sole reliance on the linked ear reference. Problems using linked ear references can be resolved by switching to bi-polar or average references.&nbsp;<br></span></p><p style="text-align: left;"><span style=""><br></span></p><p style="text-align: center;"><span style=""><br></span></p><p style="text-align: center;"><span style=""><img src="@@PLUGINFILE@@/coherence-WinEEG.png" alt="Coherence in Quantitative EEG Maps (WinEEG and iSyncBrain)" width="291" height="270" class="img-responsive atto_image_button_text-bottom"><br></span></p><p style="text-align: center;"><span style="">Figure #A - Coherence in Quantitative EEG Maps (WinEEG and iSyncBrain)<br></span></p><p style="text-align: center;"><span style=""><br></span></p><p style="text-align: center;"><span style=""><img src="@@PLUGINFILE@@/coherence-iSyncBrain.png" alt="Coherence in Quantitative EEG Maps (WinEEG and iSyncBrain)" width="427" height="379" class="img-responsive atto_image_button_text-bottom"><br></span></p><p style="text-align: center;"><span style="">Figure #B - Coherence in Quantitative EEG Maps (WinEEG and iSyncBrain)<br></span></p><p style="text-align: center;"><span style=""><br></span></p><p style="text-align: center;"><span style=""><img src="@@PLUGINFILE@@/quantitative-eeg-maps.png" alt="Phase Measures in Quantitative EEG Maps (Neuroguide)" width="712" height="539" class="img-responsive atto_image_button_text-bottom"><br></span></p><p style="text-align: center;"><span style="">Figure xx: Phase Measures in Quantitative EEG Maps (Neuroguide)<br></span></p><p style="text-align: center;"><span style=""><br></span></p>