<p></p><p>Normative
databases are constructed and validated based upon the scientific standards of
gaussianity, cross-validation, amplifier matching and peer-reviewed
publications. 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;</p><p>The database should represent the mix of
ages, gender, ethnicity, socioeconomic status and other demographic factors
present in the overall population. <b>“Representative sampling”</b> means a
demographically balanced sample of different genders, different ethnic
backgrounds, different socio-economic status and different ages.&nbsp;</p><p>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.&nbsp;</p><p>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. 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.
</p>

<p>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. Normative databases must use healthy
participants who do not have any psychological or physiological pathologies. </p><p>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;&nbsp;</p><p>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.”&nbsp;</p><p>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;</p><p><a href="https://vimeo.com/443179794" target="_blank">Click here to watch a brief in depth video of normative databases</a></p><p></p><h2><a name="_Toc35342982">Asymmetry in Quantitative EEG Maps (NeuroGuide)</a></h2><br><p></p><p style="text-align: center; "><img src="@@PLUGINFILE@@/Asymmetry.png" alt="Asymmetry" width="500" height="378" class="img-responsive atto_image_button_text-bottom"></p><h2><br></h2><p><a name="_Toc35342982"><img src="@@PLUGINFILE@@/Coherence.png" alt="Coherence in WinEEG" width="291" height="270" class="img-responsive atto_image_button_left"><br></a></p><h2><a name="_Toc35342983">Coherence measures in Quantitative EEG Maps
(WinEEG and iSyncBrain)</a></h2><img src="@@PLUGINFILE@@/Coherence%202.png" alt="Asymmetry" width="427" height="379" class="img-responsive atto_image_button_right"><br><p></p><p>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).&nbsp;Coherence measures the stability of the phase relationship between two time series, calculating the difference between two signals measured at the scalp. &nbsp;Coherence in excess is hypercoherence; coherence in deficiency is hypocoherence.&nbsp;Coherence measures do not separate phase and amplitude.&nbsp;</p><p>Unfortunately, coherence measures are also apt to be spurious and false positives are likely.&nbsp;In EEG measures, a linked ears or mastoid reference used can significantly alter the both the power and phase at each electrode site, if a high amplitude source of EEG is at one or more of the temporal electrodes. For similar reasons, any common reference coherence data must be interpreted cautiously. Even in average references, spuriously large coherences can occur from superficial dipoles at large interelectrode differences.&nbsp;&nbsp; Fein et al. (1988) argue the most diligent way to measure coherences is with reference-free recording methods, while Nunez et al (1997) agree, noting that Laplacians give the best intermediate spatial range coherence estimates.&nbsp; Finally , of import to valuation of synchrony measures offered, coherence measures do not separate phase and amplitude.<br></p><p><br></p><h4>Erroneous Coherences (Image Below)</h4><p></p><p></p><h2><a name="_Toc35342984"><img src="@@PLUGINFILE@@/Erroneous%20Coherences.png" alt="Erroneous Coherences" width="700" height="683" class="img-responsive atto_image_button_left"><br></a></h2><h2><a name="_Toc35342984"><br></a></h2><h2><a name="_Toc35342984"><br></a></h2><h2><a name="_Toc35342984"><br></a></h2><h2><a name="_Toc35342984"><br></a></h2><h2><a name="_Toc35342984"><br></a></h2><h2><a name="_Toc35342984"><br></a></h2><h2><a name="_Toc35342984"><br></a></h2><h2><a name="_Toc35342984"><br></a></h2><h2><a name="_Toc35342984"><br></a></h2><h2><a name="_Toc35342984"><br></a></h2><h2><a name="_Toc35342984"><br></a></h2><h2><a name="_Toc35342984"><br></a></h2><h2><a name="_Toc35342984">Phase Measures in Quantitative EEG Maps
(Neuroguide)</a></h2><p style="text-align: center;"><img src="@@PLUGINFILE@@/Phase.png" alt="Phase" width="501" height="379" class="img-responsive atto_image_button_text-bottom" style="font-size: 1rem;"></p><p></p><p></p><h2><a name="_Toc35342985">Quantitative “Normative” and Non-Normative Database
Validation Steps</a></h2>

<p>A quantitative database should
represent the mix of ages, gender, ethnicity, socioeconomic status and other
demographic factors present in the overall population. The method of
recruitment of normal individuals also should be considered. Poor screening
procedures will result in admitting individuals into a normal group who have
signiﬁcant clinical problems. Regardless the method of recruitment, care must
be exercised not to entice individuals to participate and falsify information
because of the ﬁnancial gain. Normative databases are to be constructed and
validated in respect to the basic scientific standards of gaussianity,
cross-validation, amplifier matching and peer-reviewed publications.</p><br><p></p>