We hear about averages all the time and often use them as the basis for measuring improvements e.g. average length of stay or average wait for an appointment. They can be very useful, as well as incredibly unuseful and sometimes just plain misleading. This post captures this very nicely in the cartoon.

With any measure we have to know the operational definition for example not just what we mean by length of stay but also the ‘average’. Knowing the average isn’t enough we need to know whether we want the mean, median or mode as described in the post. We also need to bear in mind averages can either be distorted by extreme values or ignore them depending on which type we use.

Should we therefore be using them? Blastand and Dilnot in their terrific book on using numbers (The Tiger That Isn’t, 2008, p.84) have a good summary, assuming we have defined what we mean by the average: “Should averages simply be avoided? No, because for all their hazards, sometimes we want a figure to speak for a group as a whole. And averages can be revelatory. Making them useful is mainly a question of working out which group we are interested in.”