5 Numerical summaries

Histograms provide a quick way of looking at data sets, but they lose sight of individual observations and they tend to play down ‘intuitive feel’ for the magnitude of the numbers themselves. We may often want to summarize the data in numerical terms; for example, we could use a number to summarize the general level (or location) of the values and, perhaps, another number to indicate how spread out or dispersed they are. In this section you will learn about some numerical summaries that are used for both of these purposes: measures of location are discussed in sections 4.2 to 4.5 and measures of dispersion in sections 4.6 to 4.9. In section 4.11 you will be introduced to the important concept of skewness (lack of symmetry) in a data set.