What Does "IQ" Stand For, and What Does It Mean?

    (An expanded discussion of IQ may be found here.)

What Is "IQ" ?
    "IQ" stands for " Intelligence Quotient" .
Calculating IQs:
     The IQ is equal to 100 times the Mental Age (MA) divided by the Chronological Age (CA).  

     IQ = 100 X Mental Age/Age in Years

    The mental-age concept was invented to aid in the grade placement of children. 
                                                                                  more...

Measuring IQs
    IQs are measured with IQ tests. There are a number of IQ tests available.    

Types of IQ Tests:
1.   Untimed, individually administered tests 
     (a)   Stanford Binet
            The Stanford-Binet IQ test was the first US-developed IQ test, and was introduced by Dr. Lewis M. Terman in 1916. By now, there have been six editions of the Stanford-Binet. 

Ratio IQs versus Deviation (Percentile) "IQs"
    The 1916, 1937, 1960, and 1972 editions of the Stanford-Binet utilized the concept of mental age, while the fifth edition (fourth revision) employs percentile rankings. These percentile rankings are then converted to an equivalent IQ score, called a "deviation IQ", by converting percentiles to IQs using a Gaussian distribution.

Examples of questions similar to those on the Stanford-Binet IQ test.

    (b)  Wechsler Tests
           The Wechsler tests are considered today to be the standard by which other IQ tests are judged.
          There has been a series of Wechsler Adult Intelligence Scales, beginning with the


The Wechsler tests consist of 10 or 11 (at the discretion of the test administrator) subtests, each of which has a ceiling that is 2.75 standard deviations above the mean. (The most recent edition of the Wechsler Adult Intelligence Scale, the WAIS-III, utilizes 13/14 subtests. Six of these tests are "verbal", meaning that these questions and their answers are transmitted verbally.  The six verbal subtests are:

    The other five tests (eight subtests on the WAIS-III) are "performance" (non-verbal) subtests in which the test-taker has to perform certain tasks as fast as possible.
    The five performance subtests are:

and the three additional subtests that have been added to the WAIS-III are,

    The Wechsler tests measure deviation IQs, with a standard deviation of 15 points of IQ. The Wechsler tests attempt to compensate for age-related cognitive decline by 
    Measuring 11 different facets of intelligence as they do, the Wechsler IQ tests are influenced by breadth of capability in various cognitive areas, as opposed to depth. They were designed as clinical evaluation instruments, and can detect various kinds of neurological problems.  Dr. Wechsler warned that his tests should not be used above an IQ of 130, but they are commonly used to measure IQs considerably higher than that.  One word of caution about IQ tests: they are subject to "ceiling effects" as an examinee approaches the ceilings of a test. For example, with the Wechsler tests, someone might make a perfect or almost-perfect score on several of the verbal subtests, but fail to make a perfect score on several others. Consequently, the individual in question wouldn't have bee adequately tested on those subtests for which she "hit the ceiling".
    As mentioned above, Wechsler-derived IQs are adjusted for age to offset the cognitive decline that attends aging. The graph below shows how Wechsler IQs vary with age:



Slossen Tests
    The Slossen tests are similar to the Stanford-Binet and correlate closely with them. The Slossen tests have a ceiling of 27 years of mental age.
   

     Untimed tests are often called "power" tests. Other tests are timed, proctored group tests, such as the Raven Advanced Progressive Matrices, the California Test of Mental Maturity (CTMM) and the Cattell Culture-Fair Test, which are easier to administer but are narrower in scope. (Included in this group would be the Scholastic Aptitude Test, the Graduate Record Exam, and the Miller Analogies.) Still a third class of test is the unproctored power test, such as the Mega Test, the Titan Test, and the Test for Genius. These are untimed tests in which the test-taker lays protracted siege to difficult problems that emulate the kinds of problems encountered in actual research. These tests are not universally recognized as true IQ tests because it is felt that they are susceptible to cheating, and that their scores depend upon collateral factors such as persistence and library skills as well as sheer intelligence. 
    IQ's were originally measured using the MA/CA concept: IQ = MA/CA. If you were 10 years old and earned Mental Age scores on IQ tests equal to those of 16-year-olds, your IQ would be 16/10 X100, or 160. This seemed to work well enough for children, but it encountered 
    IQ tests have been under attack since their inception. It is, perhaps, counter-intuitive and unpopular that a test requiring an hour or two can establish the upper bounds of one's intellect for a lifetime. However, although they're not infallible, for adults, they do a remarkably good job of generating a score that will remain more or less constant throughout life.

Can Intelligence Be Measured With a Single Number?
    Yes and no. One of the most serious criticisms of using a single number to assess intelligence is that people may be stronger in certain areas such as verbal skills, logical aptitude or spatial visualization than in others. Drs. Richard Feynman and Albert Einstein would be examples of geniuses who were reputed to be extremely strong mathematically while being relatively weak verbally. More commonly, though, purely intellectual abilities tend to be uniformly high or uniformly low in a given individual, consistent with the concept of an underlying "g" or "general intelligence" that powers all the specialized intellectual aptitudes. In addition, there are several sub-factors such as verbal, spatial, Still, this doesn't happen with everyone, and the exceptions, like Richard Feynman and Albert Einstein, are very important. Tests like the Wechsler Adult Intelligence Scale (WAIS) consist of a number of subtests that are scored separately and can measure the profile for an individual. (Dr. Howard Gardner has defined seven types of intelligence, while Dr. Robert Sternberg has identified three.)
    It's also easier to make an IQ score that's lower than your true IQ than it is to make a score that's higher. Taking a test on a bad day, or spending too much time on a few difficult items could artificially lower one's score. The best results are obtained when more than one test is administered.

What Does Adult IQ Mean?
    Generally, one's mental age stops rising rapidly when one reaches the latter teens--e. g., 16. Consequently, on some IQ tests, "16" was taken as the chronological-age divisor in an IQ calculation for adults. The Wechsler Adult Intelligence Scale is calibrated for all ages up to 70, with chronological-age divisors appropriate to every age 70 or below.
    The average IQ is, by definition, 100. To get an idea what this means, someone with an IQ of 80 or below is considered to be marginally able to cope with the adult world. People with IQ's of 80 or below typically work as unskilled laborers such as lawn maintenance and trash pickup. They generally need help from friends or family to manage life's complications. About 10% of the population has an IQ of 80 or below.
    People with IQ's of 80-90 are a little on the slow side but may be found in fast-food restaurants, day-care centers, etc. They may also be found in unskilled jobs. About 16% of the population has IQ's in this range.
    People with IQ's of 90-110 generally occupy semi-skilled positions, including typists, receptionists, assembly line workers, and checkout clerks. They are able to keep up with the world, and comprise about 46% of the public.
    People with IQ's in the 110 to 120 range fill the skilled trades and include some tool and die makers, teachers, and Ph. D.'s among their ranks. They also make up 16% of the population.
    People with IQ's of 120 and above tend to staff the professions as doctors, dentists, lawyers, teachers, and college professors. They fall in the upper 10% of the population.

Ratio IQ's Versus Deviation-IQ's
    Before going any higher in the IQ scale, it's necessary to talk about ratio-IQ's versus deviation-IQ's. As mentioned above, IQ's were defined as the ratio of Mental Age to chronological age.

    The average IQ of all college professors is 130, which lies within the upper 3% of the general public.
 

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