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| quote: | IQ scores are expressed as a number normalized so that the average IQ in an age group is 100 — in other words an individual scoring 115 is above-average when compared to similarly aged people. It is common, but not invariable, practice to standardize so that the standard deviation of scores is 15 or 16 ( 24 is used occasionally as well ). Tests are designed so that the distribution of IQ scores is Gaussian, that is to say that it follows a bell curve. A difference has been documented between the IQ score distributions of left-handed and right-handed test subjects; the distribution in left-handed people tends to cluster at the two extremes of the IQ scale.
(The following numbers apply to IQ scales standard deviation σ = 15.) Roughly 68% of the population has an IQ between 85 and 115. The "normal" range, or range between -2 and +2 standard deviations from the mean, is between 70 and 130, and contains about 95% of the population. A score below 70 may indicate mental retardation, and a score above 130 may indicate intellectual giftedness. Retardation may result from normal variation or from a genetic or developmental malady; analogously, some otherwise normal people are very short, and others have dwarfism. Giftedness appears to be normal variation; autistic savants have often astonishing cognitive powers but below-average IQs.
It has been observed that scores outside the range 55 to 145 must be cautiously interpreted because there are smaller numbers of respondents with which to make comparisons in those ranges. Moreover, at such extreme values, the normal distribution is a less accurate estimate of the true IQ distribution.
In actuality there is a higher percentage of the population measured at 3sd+ levels on the test than the probabilities of the normal distribution would predict. Some IQ scoring procedures may attempt to integrate such clusters of statistical outliers into the curve by adjusting the scores so that they better represent actual probabilities (according to Silverman) and in these cases, scores around 145 and above may actually have been notably higher, were they not so adjusted. |
| quote: | | Although online IQ tests have become wildly popular with the explosion of the internet in recent years, they are highly inaccurate. Comparing results among a large set of people shows a common factor: most scores are above 110. Of course, such tests automatically measure very few people in the 70 to 90 range, and hence create a strong upward distortion. Many of these websites do not show the results immediately and instead attempt to sell certificates showing the results. |
And since we are talking about Googooly:
| quote: | About 75-80 percent of mental retardation is familial (runs in families), and 20-25 percent is due to organic problems, such as chromosomal abnormalities or brain damage.[2] Mild to severe mental retardation is a symptom of several hundred single-gene disorders and many chromosomal abnormalities, including small deletions. Based on twin studies, moderate to severe mental retardation does not appear to be familial, but mild mental retardation does. That is, the relatives of the moderate to severely mentally retarded have normal IQs, whereas the families of the mildly mentally retarded have low IQ.
IQ score ranges (from DSM-IV):
* mild mental retardation: IQ 50-55 to 70; children require mild support; formally called "Educable Mentally Retarded"
* moderate retardation: IQ 35-40 to 50-55; children require moderate supervision and assistance; formally called "Trainable Mentally Retarded"
* severe mental retardation: IQ 20-25 to 35-40; can be taught basic life skills and simple tasks with supervision
* profound mental retardation: IQ below 20-25; usually caused by a neurological condition; require constant care
The rate of mental retardation is higher among males than females, and higher among blacks than whites, according to a 1991 U.S. Centers for Disease Control and Prevention (CDC) study.[3] By race, the overall rate was 16.6% for blacks and 6.8% for whites. Rates of mental retardation for black males, the group with the highest rates, were 1.7 times higher than black females, 2.4 times higher than white males, and 3.1 times higher than white females. |
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