- Standardized and other formal assessments
is typically similar, with many students scoring close to the mean, and fewer scoring much higher or lower than the
mean. When the distribution of scores looks like the bell shape shown in Exhibit 19 it is called a normal
distribution. In the diagram we did not draw in the scores of individual students as we did in Exhibit 20, because
distributions typically only fall on a normal curve when there are a large number of students; too many to show
individually. A normal distribution is symmetric, and the mean, median and mode are all the same.
Exhibit 22: Bell shaped curve of normal distributionNormal curve distributions are very important in education and psychology because of the relationship between
the mean, standard deviation, and percentiles. In all normal distributions 34 per cent of the scores fall between the
mean and one standard deviation of the mean. Intelligence tests often are constructed to have a mean of 100 and
standard deviation of 15 and we illustrate that in Exhibit 15.
Exhibit 23: Normal distribution for an IQ test with mean 100 and standard
deviation 15