All persons do not have the same intellectual capacity. They vary in their intellectual ability. Some are exceptionally bright and some are below average. Some possess high IQ range while others have average or below average.
All the scores gradually and symmetrically decline towards both the sides but never touch the X-axis.
(i) 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.
(ii) On the basis of IQ, people are classified in different groups. It is clear that only 2.2 percent people who possess above 130 IQ range are very intelligent or very superior, their IQ score is more than 130.
(iii) People falling between 90-109 IQ range are considered as average. The mean IQ score in a population is 100. People with IQ scores in the range of 90-110 have normal intelligence.
(iv) Those with IQ below 70 are suspected to have ‘mental retardation’. Mental retardation refers to sub-average intellectual functioning. The behaviour is maladaptive and manifest in four forms i.e., mild, moderate, severe and profound mental retardation.
The extreme right also lie to 2.2 percent population which are known as gifted i.e., they enjoy exceptional intelligence, exceptional talent and exceptional creativity.
Classification of People on the Basis of IQ
| IQ Range |
Descriptive Label |
Percent in the population |
| Above 130 |
Very superior |
2.2 |
| 120-130 |
Superior |
6.7 |
| 110-119 |
High average |
16.1 |
| 90-109 |
Average |
50.0 |
| 80-89 |
Low average |
16.1 |
| 70-79 |
borderline |
6.7 |
| Below 70 |
mentally challenged/retarded |
2.2 |
