Asked by: Mary Jackson, London
Known to statisticians as the Gaussian or Normal distribution, the bell curve is routinely used to describe everything from the outcome of dice rolls to the weights, heights and IQs of randomly selected groups of people.
The reason it's so common is because many phenomena have typical or 'mean' values due to their underlying causes (such as genetics), plus random variation caused by a host of chance effects. Mathematicians have proved that if one collects lots of samples of the same phenomenon, each with their own means and scatter, the combined result will be the familiar bell-shaped spread of values.
Robert is a science writer and visiting professor of science at Aston University.