Chapter 3 Measures of Shape

A measure of shape tells us how symmetrical or asymmetrical a set of data is. Skewness is a measure of shape, and can be negative (skewed to the left, or negatively skewed), 0 (symmetrical), or positive (skewed to the right, or positively skewed). This can be demonstrated via the histograms below:

It is also useful to know whether our data are unimodal (one mode), bimodal (two modes), or multimodal (more than two modes). For example:

Ascertaining the modality of a distribution can be useful for a number of reasons. For example, if we identify that a distribution is bimodal, it can indicate to us that there could be two distinct groups within the data.