Most people would probably agree that individuals vary in "brightness" or "intelligence," in their capacity for adaptive thinking and action. There is considerable controversy about the extent to which these variations in intelligence are genetically determined, the extent to which they remain constant throughout the life cycle, and the point in development at which such variations become measurable and predictable entities. The reliability and validity of infant intelligence tests are questionable. During the first two years of life, there is rarely consistency between an infant's performances on the same test at different times, or between an individual's performance on different tests given at the same time. At any given point in development, it is not possible to predict from a child's score on one test what his or her score might be on another test. Infants test scores are poor indices of performance on intelligence tests for older children such as the Stanford Binet and the Wechsler Intelligence Scale for Children (WISC). This may be explained by the fact that infant tests measure primarily sensorimotor functions, while tests at later age levels are based on verbal and reasoning skills.
A general rule of thumb in interpreting infant intelligence test scores is that their predictive value increases directly as the age of the child increases and inversely with the amount of time between successive testings. Infant tests can also reveal children who are at the extremes, those who are exceedingly advanced or who are exceedingly slow. Where infant tests are less useful is in the middle range of intellectual ability, where finer discriminations are necessary. Unfortunately, it is in just this middle range where tests are most needed, since the experienced clinician does not usually need a mental test to recognize the exceptional child at either end of the ability scale.
General intellectual functioning is defined as an intelligence quotient (IQ) obtained by assessment with one or more of the individually administered general intelligence tests. Figure 14.4 outlines the suggested age at which many of these available tests are applicable. Each test measures specific areas and has particular strengths and weaknesses. The interested reader is referred to literature cited at the end of this chapter for more detailed information.
Significantly subaverage intellectual functioning is defined as an IQ of 70 or less on an individually administered IQ test. Since any measurement is fallible, an IQ score is generally thought to involve an error of measurement of approximately 5 points. Hence, an IQ of 70 is considered to represent a band or zone of 65 to 75. An IQ level of 70 was chosen because most people with IQs below 70 require special services and care, particularly l—1—I—1—I—1—I—1—I-1-1-1-1-1-1-1-1-1-1-1-[
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For as much as we believe we train our brains and give them a good workout, we seldom actually do it on a regular basis. In most cases, our brains are not used in a balanced way. We're creatures of habit. We find a way to do things that we consider comfortable and we seldom change our ways.