How to Lie with Statistics – Part 2: The Well-Chosen Average

Continuing with my previous post, here I summarize Chapter 2 of the book How to Lie with Statistics. This chapter is titled, The Well-Chosen Average.

The key thought in this chapter is to remember to ask more questions when you hear or read about some “average”, such as the “average” income, the “average” pay, or “average” price – just to name a few. The first thing to remember is to ask, what kind of average and how that metric is calculated. An arithmetic average, which you simply divide a total amount by the number of observations, will yield a different outcome compared with the median average, which gives you the middle amount after sorting the data in ascending or descending order.

When averages are particularly highlighted, that should alert us to be on the lookout that a deceptive figure may be coming our way. If you are not told exactly how he average is calculated, do not readily accept the conclusions being submitted.

Any dataset that is skewed, that is, when graphed you see that the data particularly bunched in one side, the relevant “average” is the median. The arithmetic average will always be deceptive in such skewed data. So, be aware, be alert when you come across the “average” something.