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(Study Material) Psychology Study Material (Individual Differences in Intelligence)

Submitted by IASguru on Sat, 2009-06-06 12:40

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Psychology Study Material: Individual Differences in Intelligence

INDIVIDUAL DIFFERENCES IN INTELLIGENCE

Why are some people more intelligent than others? Is it due to their heredity, or is it due to the influence of environmental factors?

Intelligence: Interplay of Nature and Nurture

The evidence for hereditary influences on intelligence comes mainly from studies on twins and adopted children. The intelligence of identical twins reared together correlate almost 0.90. Twins separated early in childhood also show considerable similarity in their intellectual, personality and behavioral characteristics. The intelligence of identical twins reared in different environments correlate 0.72, those of fraternal twins reared together correlate almost 0.60, and those of brothers and sisters reared together correlate about 0.50, while siblings reared apart correlate about 0.25. Another line of evidence comes from the studies of adopted children, which show that children’s intelligence is more similar to their biological rather than adoptive parents.

With respect to the role of environment, studies have reported that as children grow in age, their intelligence level tends to move closer to that of their adoptive parents. Children from disadvantaged homes adopted into families with higher socioeconomic status exhibit a large increase in their intelligence scores. There is evidence that environmental deprivation lowers intelligence while rich nutrition, good family background, and quality schooling increases intelligence. There is a general consensus among psychologists that intelligence is a product of complex interaction of heredity (nature) and environment (nurture). Heredity can best be viewed as something that sets a range within which an individual’s development is actually shaped by the support and opportunities of the environment.

Assessment of Intelligence

In 1905, Alfred Binet and Theodore Simon, made the first successful attempt to formally measure intelligence. In 1908, when the scale was revised, they gave the concept of Mental Age (MA), which is a measure of a person’s intellectual development relative to people of her/his age group. A mental age of 5 means that a child’s performance on an intelligence test equals the average performance level of a group of 5-year olds. Chronological Age (CA) is the biological age from birth. A bright child’s MA is more than her/his CA; for a dull child, MA is below the CA. Retardation was defined by Binet and Simon as being two mental age years below the chronological age.

In 1912, William Stern, a German psychologist, devised the concept of Intelligence Quotient (IQ). IQ refers to mental age divided by chronological age, and multiplied by 100.

IQ = (MA/CA) * 100

The number 100 is used as a multiplier to avoid the decimal point. When the MA equals the CA, the IQ equals 100. If MA is more than the CA, IQ is more than 100. IQ becomes less than 100 when the MA is less than the CA. For example, a 10-year-old child with a mental age of 12 would have an IQ of 120 (12/10 100), Chapter 1 • Variations in Psychological Attributes 11 whereas the same child with an MA of 7 would have an IQ of 70 (7/10 100). The average IQ in the population is 100, irrespective of age.

IQ scores are distributed in the population in such a way that the scores of most people tend to fall in the middle range of the distribution. Only a few people have either very high or very low scores. The frequency distribution for the IQ scores tends to approximate a bell shaped curve, called the normal curve. This type of distribution is symmetrical around the central value, called the mean. The distribution of IQ scores in the form of a normal distribution is shown below:

The mean IQ score in a population is 100. People with IQ scores in the range of 90–110 have normal intelligence. Those with IQ below 70 are suspected to have ‘mental retardation’, while persons with IQ above 130 are considered to have exceptional talents All persons do not have the same intellectual capacity; some are exceptionally bright and some are below average. One practical use of intelligence test is to identify persons at the extremes of intellectual functioning. If you refer to Table 1.1, you will notice that about 2 per cent of the population have IQ above 130, and a similar percentage have IQ below 70. The persons in the first group are called intellectually gifted; those in the second group are termed mentally challenged or mentally retarded. These two groups deviate considerably from the normal population in respect of their cognitive, emotional, and motivational characteristics.