Kondacs A, Szabó M
Department of Neurology I., Pándy Kálmán County Hospital, Semmelweis, Hungary.
Clin Neurophysiol. 1999 Oct;110(10):1708-16. doi: 10.1016/s1388-2457(99)00122-4.
Forty-five healthy adult volunteers underwent repeated qEEG examinations with retest intervals 25-62 months in order to investigate the long-term intra-individual variability of several qEEG features such as, absolute and relative power, power asymmetry, coherence, mean and peak frequency and entropy. Prior to any computations all parameters were transformed to Z-scores on the basis of a normal database.
Correlation coefficients were used to test the effect of the time on the test-retest differences. Correlation coefficients were also computed between baseline and retest values, as a measure of intra-individual stability, to make our results comparable to most literature data. By computing the standard deviations for test-retest differences, the intra-individual variabilities of the examined parameters were obtained in the unit of inter-individual variability of normal population. The same calculations were carried out with values obtained from the odd and even numbered epochs of the same EEG sections. This way, that portion of the intra-individual variability was estimated that might be introduced even by chance only when the epochs were selected randomly from the same section of EEG conforming to selection criteria.
As for our results, further increase of test-retest differences with time after 25 months might be so insignificant that it could not be demonstrated in our test material. The long-term intra-individual variability for most parameters, especially for total absolute power and alpha mean frequency, was less than the inter-individual variability in the normal population. The moment-to-moment variability was least in the case of the absolute power.
Estimates for intra-individual variability expressed this way in Z-scores might easily be used in the follow-up of patients even for a few years.
45名健康成年志愿者接受了重复的定量脑电图（qEEG）检查，复测间隔为25 - 62个月，以研究几个qEEG特征的长期个体内变异性，如绝对功率和相对功率、功率不对称性、相干性、平均频率和峰值频率以及熵。在进行任何计算之前，所有参数都基于一个正常数据库转换为Z分数。
使用相关系数来测试时间对重测差异的影响。还计算了基线值和重测值之间的相关系数，作为个体内稳定性的一种度量，以使我们的结果与大多数文献数据具有可比性。通过计算重测差异的标准差，以正常人群个体间变异性为单位获得所检查参数的个体内变异性。对来自同一脑电图段奇数和偶数时段获得的值进行相同的计算。通过这种方式，估计了仅在从符合选择标准的脑电图同一段中随机选择时段时可能偶然引入的个体内变异性部分。
就我们的结果而言，25个月后重测差异随时间的进一步增加可能非常不显著，以至于在我们的测试材料中无法证明。大多数参数的长期个体内变异性，特别是总绝对功率和α平均频率，小于正常人群的个体间变异性。绝对功率情况下的瞬间变异性最小。
以这种方式用Z分数表示的个体内变异性估计值甚至在几年的患者随访中也可能很容易使用。
