EVIDENCE THAT DYSLEXIA MAY REPRESENT THE LOWER TAIL OF A NORMAL-DISTRIBUTION OF READING-ABILITY
EVIDENCE THAT DYSLEXIA MAY REPRESENT THE LOWER TAIL OF A NORMAL-DISTRIBUTION OF READING-ABILITY
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DOI：
10.1056/nejm199201163260301
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发表时间：
1992-01-16
影响因子：
158.5
通讯作者：
MAKUCH, R
中科院分区：
文献类型：
--
作者：
SHAYWITZ, SE;ESCOBAR, MD;MAKUCH, R
背景诵读困难现在被广泛认为是一种生物学上的障碍，与其他不太具体的阅读问题不同。根据这一观点，阅读能力被认为是遵循双峰分布，与诵读困难作为较低的模式。我们假设，相反，阅读能力遵循正态分布，与诵读困难在连续的低端。我们使用的数据来自康涅狄格州纵向研究，414名康涅狄格州儿童谁进入幼儿园在1983年的抽样调查，并作为一个纵向队列。阅读障碍是根据差异分数来定义的，差异分数代表了实际阅读成绩与根据智力测量预测的成绩之间的差异。数据来自1、3、5年级的智力测试和1至6年级每年的成绩测试。每个孩子有108个可能的差异分数（[3 x 3岁] x [2 x 6岁]），这些分数是基于三年中每一年的能力分数（全量表、语言和表现10）和六年中每一年的两个成绩分数（阅读和数学）的组合。我们证明了每个差异分数都遵循单变量正态分布，并且两个不同差异分数的相互关系遵循双变量正态分布。最多，108个差异分数中只有9个（8.3%）和3402对差异分数中的171个（5%-0%）与预期分数有显著差异（在5%的水平上）-分别在单变量和双变量正态分布数据的预期值范围内。我们还研究了随着时间的推移，诵读困难的稳定性。正态分布模型预测（数据显示），在一年级被归类为阅读障碍的25名儿童中，只有7名（28%）在三年级也被归类为阅读障碍。包括诵读困难在内的阅读困难，是正常阅读能力的连续体的一部分。阅读障碍并不是一种全有或全无的现象，而是像高血压一样，有程度的发生。阅读障碍诊断中固有的变异性可以用正态分布模型进行量化和预测。
Background. Dyslexia is now widely believed to be a biologically based disorder that is distinct from other, less specific reading problems. According to this view, reading ability is considered to follow a bimodal distribution, with dyslexia as the lower mode. We hypothesized that, instead, reading ability follows a normal distribution, with dyslexia at the lower end of the continuum.Methods and Results. We used data from the Connecticut Longitudinal Study, a sample survey of 414 Connecticut children who entered kindergarten in 1983 and were followed as a longitudinal cohort. Dyslexia was defined in terms of a discrepancy score, which represents the difference between actual reading achievement and achievement predicted on the basis of measures of intelligence. Data were available from intelligence tests administered in grades 1, 3, and 5 and achievement tests administered yearly in grades 1 through 6. For each child there were 108 possible discrepancy scores ([3 x 3 years] x [2 x 6 years]) based on combinations of the ability scores (full-scale, verbal, and performance 10) in each of three years and two achievement scores (reading and mathematics) in each of six years. We demonstrated that each of the discrepancy scores followed a univariate normal distribution and that the interrelation of two different discrepancy scores followed a bivariate normal distribution. At most, only 9 of 108 discrepancy scores (8.3 percent) and 171 of 3402 pairs of discrepancy scores (5-0 percent) were significantly different (at the 5 percent level) from the expected scores - well within the expected values for data with univariate and bivariate normal distributions, respectively. We also examined the stability of dyslexia over time. The normal-distribution model predicted (and the data indicated) that only 7 of the 25 children (28 percent) classified as having dyslexia in grade 1 would also be classified as having dyslexia in grade 3.Conclusions. Reading difficulties, including dyslexia, occur as part of a continuum that also includes normal reading ability. Dyslexia is not an all-or-none phenomenon, but like hypertension, occurs in degrees. The variability inherent in the diagnosis of dyslexia can be both quantified and predicted with use of the normal-distribution model.