“Intelligence” 

Competing definitions	History	Intelligence Quotient (IQ)	The "Bell Curve"
Components	The “g” factor	Political issues	Factors in Educational Achievement
	Can intelligence be taught?	Multiple Intelligences

“Intelligence” is in quotes because it is a fraught subject for technical and political reasons, raising issues of its nature, how it is tested, and the uses of results.  This cursory overview is even less reliable than other pages on this site.

The idea

Intelligence is meant to be a generalised measure of overall ability, or potential ability: its proponents claim that it is getting at an underlying feature which is independent of specific skill development or learning achievement.  

Competing definitions

The problem is that it is difficult to get a consensus about what "intelligence" actually is:

 "The power of good responses from the point of view of truth or fact" (Thorndike)

 "A biological mechanism by which the effects of a complexity of stimuli are brought together and given a somewhat unified effect in behavior" (Peterson)

 "The ability to carry on abstract thinking" (Terman)

 "The ability to adapt oneself adequately to relatively new situations in life" (Pintner)

 "The capacity for knowledge, and knowledge possessed" (Henmon)

 "The capacity to acquire capacity" (Woodrow)

History

• Francis Galton (1884) measured head size, reaction time etc., but found no correlations

• Alfred Binet (1905 on) devised tests to determine ineducability (to meet the requirements of a new French law prescribing schooling for all educable children) and formulated the idea of "Mental Age" from which developed the idea of the "Intelligence Quotient" (see below)

• Lewis Terman (at Stanford University) adapted and standardised the Binet tests for American children (1916, and routinely revised since) known as the "Stanford-Binet" tests.

• David Wechsler developed the Wechsler Adult Intelligence Scale in 1939

Intelligence Quotient (IQ)

IQ =	Mental Age x 100
	Chronological Age

So if the Mental Age = Chronological Age, IQ = 100, the notional average. The distribution of IQ supposedly follows a normal distribution curve (or "Bell Curve"), and assessment of "superiority" and "inferiority" is determined by the number of statistical Standard Deviations above and below the mean.

The “Bell Curve”

<20	20-34	35-49	50-69	70-89	90-109	110-129	130+
Profound learning difficulty	Severe learning difficulty	Moderate learning difficulty	Mild learning difficulty	Low normal	Normal	High normal	“Genius”

The Bell curve referred to in Herrnstein and Murray's (1995) famous (or notorious) book is simply the normal distribution curve which IQ tests were set up to plot. 68% of the population come within one standard deviation of the mean, and 95% within two standard deviations.

Components

The 1986 Stanford-Binet Test —one of the accepted standard tests—examines four broad areas of intelligence, which are supposed to be independent of each other, and not culture bound.

The g (for "general") factor is arrived at by factor analysis of results from tests and is suggested as the main underlying component, supplemented by components relating to more specific aptitudes. Critics suggest g is an artefact of method, since Spearman was a statistician rather than a psychologist, although it is conceded that “intelligence” may have a hierarchical structure.

At the other end of the scale is the notion of multiple intelligences, suggested by Howard Gardner.

Clearly, high intelligence may be expected to correlate significantly with educational achievement. The correlation is positive, but declines substantially as students proceed through the system:

 Figures from US. terminology revised for UK: from Atkinson et al (1993)

As the correlation figures show, intelligence alone is not sufficient to account for academic achievement: it is certainly necessary, but beyond a certain threshold, it is by no means clear how much.

As education progresses, other factors come into play, such that the limits are determined by the strength of the weakest link in the chain.

Political issues

• Intelligence has been a fraught political issue, ever since Francis Galton attempted to measure ability to support his eugenic theories. Early abuses in the United States included compulsory sterilisation of people with low IQ (Gould, 1984).

• In the UK, Sir Cyril Burt's work on IQ was the basis of selection at 11+, in the 1944 Education Act. In the 1970s, Burt was accused of fraudulent results because some of his findings were too significant: he appears to have been rehabilitated, but there are still some unanswered questions.

• Arthur Jensen (1969) was accused of racism when he suggested that white children were more intelligent than blacks (and that Asian children were brighter than either). Latterly, the controversy has been revived by Herrnstein and Murray (1995) and publication of Chris Brand's book The g Factor was abandoned at the last minute in 1996 because of concerns about his self-confessed "scientific racism"
     

For critical reviews of these issues see Montagu (1999) and Richardson (2000)

Can intelligence be taught?

There is considerable debate over the hereditary component in intelligence, and the picture is getting more complicated all the time, but at least one school believes that intelligence can largely be identified with "problem-solving skills" or even forms of pattern recognition and that as such it can be taught. (Feuerstein, 1980—see Sharron’s more accessible account— Soden 1994)