Mean and Median - Communicating Data with Tableau - page 100

Chapter 6. Mean and Median
“...like a statistician who drowned in a lake of average depth six inches.”
—Anonymous
Try to think of a time when you listened to a presentation about data that didn't include
either an average or a median value. They're almost as common as percentages. Whether
we're tracking home prices, the stock market, student test scores, or the price of gasoline, we
come face to face with the notion of central tendency on a regular basis.
Why are they so commonly used? As humans, we have a hard time processing a simple list
of more than a half dozen values, let alone reams and reams of raw data. The attractiveness
of these measures of central tendency is that they condense a lot of data into digestible
morsels that carry with them the notion of “typical.”
As useful as these statistics can be to communicate data, they need to be handled with care.
In this chapter, we'll see how they can be put to good use, but we'll also see how they can
mislead.
The three main measures of central tendency are mean, median, and mode. Let's start with
their definitions:
▪ The mean (or average) is determined by summing all of the values in a data set and di-
viding by the number of values. The mean is considered a “representative value,” mean-
ing if you replaced each value in the data set with the mean, the overall sum wouldn't
change.
▪ The median is the middle value in a data set in which the values have been placed in or-
der of magnitude. Thus, half the values in the data set are less than the median, and half
are greater.
▪ The mode is the most commonly occurring value in a data set.
Before diving into the data, let's clarify that the goal of our discussion about mean and medi-
an isn't to recap our freshman statistics courses. This topic is for practitioners, so we'll focus
on the use of these statistics in communicating data.