Background

First, I will talk about the nature of intelligence. It is multifaceted, meaning it can be expressed in many domains. It is also functional. That is, finishing tasks or solving problems are usually results of intelligent behavior. In the process, one’s cognitive skill is revealed. Intelligence, like nearly every psychological trait in which individuals differ, reflects a combination of heredity and environment. IQ tests were invented to measure intelligence level and had evolved over the century. Alfred Binet in France invented the very first IQ test, it was called the Binet’s Scale. It was then translated and revised by Lewis Terman of Stanford University, USA. The American version was called the Stanford-Binet Scale. The most significant modification was intelligence quotient (IQ), which quantify intellectual functioning to allow comparison. Binet’s Scale and Stanford Binet’s Scale were linguistically and culturally biased toward native-born English speakers. David Wechsler invented the Wechsler-Bellevue test, which minimized the bias. Wechsler Adult Intelligence Scale, third edition and Wechsler Intelligence Scale for Children are latest modifications. Distribution of IQ scores is shown by a bell-shaped curve. The mean is 100. The standard deviation is 15. IQ 85-115 is the average range, which most people’s scores lie in (Western, 2002).