Measures of dispersion

Determining the variance

The average of the square of the difference between each data and the mean

Determining the standard deviation

Measure of dispersion relative to its mean, which is measured in the same unit of the original data

Formula of interquartile range

Interquartile range of a set of grouped data

Can be determined from ogive by finding first quartile and third quartile first

Calculating range

Midpoint of the highest class – midpoint of the lowest class

Symmetric distribution

The median lies in the middle of the box and the whiskers are about the same length on both sides of the box

Left-skewed distribution

The median cuts the box into two different sizes, If the left side of the box is longer, then the data distribution is left-skewed

Right-skewed distribution

The median cuts the box into two different sizes, if the right side of the box is longer, then the data distribution is right-skewed

Example of box plot

Example of data representation