Continuous variation

This is a gradual change in a characteristic across a population, it could be human height, mass and shoe size.

Continuous variation is represented as a histogram.

A histogram should show normal distribution, with most individuals around the average value and a few at the extremes.

Height category on x axis range from less than 130 cm to more than 174 cm. Number of people in each category is y axis. Graph rises steadily peaking between 150-154 cm, then falls steadily.

Discontinuous variation

The population can be clearly divided into discrete groups.

Individuals will fit into a group – there are no intermediates.

The ability to roll your tongue, blood group (A, B, AB, O) and hand dominance (left or right handed) are all examples.

Discontinuous variation is represented as a bar chart.

Blood group graph. X-axis has blood groups A, B, AB and O. Y axis is percentage of population from 0-50.  A is just over 40%, B is just under 10 %, AB is less than 5% and O is over 45%.