It assumes that any human characteristic is spread in a normal way across the general population. When the incidence of the characteristic is plotted on a graph, it forms a curve of normal distibution. The majority of people will fall in the middle of the graph, and the minority will fall at either extreme.
Normal and abnormal behaviour is viewed the same. If it is at the top or bottom 2.5% or 2 standard deviations away from the the mean, it is considered as abnormal. E.g. 65% of the population have an I of between 85 an and 115, the majority (95%) have an IQ between 70 and 130, therefore those who have an IQ lower that 70 or higher than 130 are considered abnormal.
- It does not tell us the difference between desirable behaviour that is statistically infrequent and undesirable behaviour that is frequent, Someone of an IQ of over 130…