Medical Investigation of Neurodevelopmental Disorders (M.I.N.D.), Institute, University of California-Davis Medical Center, 2825 50th Street, Sacramento, CA 95817, USA.
J Neurodev Disord. 2009 Mar;1(1):33-45. doi: 10.1007/s11689-008-9001-8.
Intelligence testing in children with intellectual disabilities (ID) has significant limitations. The normative samples of widely used intelligence tests, such as the Wechsler Intelligence Scales, rarely include an adequate number of subjects with ID needed to provide sensitive measurement in the very low ability range, and they are highly subject to floor effects. The IQ measurement problems in these children prevent characterization of strengths and weaknesses, poorer estimates of cognitive abilities in research applications, and in clinical settings, limited utility for assessment, prognosis estimation, and planning intervention. Here, we examined the sensitivity of the Wechsler Intelligence Scale for Children (WISC-III) in a large sample of children with fragile X syndrome (FXS), the most common cause of inherited ID. The WISC-III was administered to 217 children with FXS (age 6-17 years, 83 girls and 134 boys). Using raw norms data obtained with permission from the Psychological Corporation, we calculated normalized scores representing each participant's actual deviation from the standardization sample using a z-score transformation. To validate this approach, we compared correlations between the new normalized scores versus the usual standard scores with a measure of adaptive behavior (Vineland Adaptive Behavior Scales) and with a genetic measure specific to FXS (FMR1 protein or FMRP). The distribution of WISC-III standard scores showed significant skewing with floor effects in a high proportion of participants, especially males (64.9%-94.0% across subtests). With the z-score normalization, the flooring problems were eliminated and scores were normally distributed. Furthermore, we found correlations between cognitive performance and adaptive behavior, and between cognition and FMRP that were very much improved when using these normalized scores in contrast to the usual standardized scores. The results of this study show that meaningful variation in intellectual ability in children with FXS, and probably other populations of children with neurodevelopmental disorders, is obscured by the usual translation of raw scores into standardized scores. A method of raw score transformation may improve the characterization of cognitive functioning in ID populations, especially for research applications.
儿童智力障碍（ID）的智力测试存在重大局限性。广泛使用的智力测试，如韦氏智力量表，其常模样本很少包括足够数量的 ID 受试者，无法在极低能力范围内提供敏感的测量，而且极易受到地板效应的影响。这些儿童的智商测量问题妨碍了对其优势和劣势的描述，在研究应用和临床环境中，对认知能力的估计较差，在评估、预后估计和干预计划方面的应用有限。在这里，我们在一个大的脆性 X 综合征（FXS）患儿样本中检查了韦氏儿童智力量表（WISC-III）的敏感性，FXS 是遗传性智力障碍的最常见原因。对 217 名患有 FXS 的儿童（6-17 岁，83 名女孩和 134 名男孩）进行了 WISC-III 测试。我们使用从心理公司获得的许可原始规范数据，使用 z 分数转换计算每个参与者的实际分数与标准化样本的偏差的归一化分数。为了验证这种方法，我们将新的归一化分数与通常的标准分数与适应行为（韦氏适应行为量表）和特定于 FXS 的遗传指标（FMR1 蛋白或 FMRP）之间的相关性进行了比较。WISC-III 标准分数的分布显示，尤其是男性（在各个子测试中占 64.9%-94.0%），有很大比例的参与者出现了明显的倾斜和地板效应。通过 z 分数归一化，消除了地板问题，分数呈正态分布。此外，我们发现认知表现与适应行为之间，以及认知与 FMRP 之间的相关性，当使用这些归一化分数时，与使用通常的标准化分数相比，得到了很大的改善。这项研究的结果表明，在 FXS 儿童以及可能在其他神经发育障碍儿童群体中，智力能力的显著差异被将原始分数转换为标准分数的通常方法所掩盖。原始分数转换方法可能会改善 ID 人群的认知功能特征，特别是对于研究应用。
