Pitch the pie! Ban the bar!

Steve Simon


**[StATS]: Pitch the pie! Ban the bar! (June 5, 2003)**.

*This is an outline of a speech that I gave to Bluejacket Toastmasters on June 5

I work a lot with numbers and I’ve found that there is usually a good way to display those numbers and a bad way. Here’s an example.

It’s a pie chart with bright bold colors and a deep 3-D effect. Is this a good way to display the data? WRONG! You should pitch the pie.

Here’s another example.

It’s a bar chart with big bold purple bars. Is this a good way to display the data? WRONG AGAIN! You should ban the bar.

These charts are useful once in a while

But you can’t just toss the numbers onto a sheet of paper and hope that it will work out well. You have to plan things. There are two things that can help:

  1. a little bit of rounding
  1. a little bit of re-ordering.

Costs of pet ownership example

Shown below is a table loosely adapted from a web page on pet care. I’ve taken a few liberties with some of the numbers to simplify this discussion

^1^includes items like cost of the pet

The initial cost would include the cost of the pet

Look at this table and tell me what patterns you see. A few patterns might appear

But it takes a lot of squinting and staring to discover these patterns.

This table needs some work. The first thing is to do some rounding.


Rounding is important because it reduces the strain on your brain. You don’t have to work so hard to uncover patterns in the data.

When you look at a table of numbers

For example

The respective numbers are

317.24 193.08

Take some time to subtract here. This would tell you how much you would save on yearly vet bills if you got a cat instead of a dog.

Let’s see

You can simplify life by rounding the data to one or two significant figures. Here are the rounded costs

320 190

If I asked you to subtract those two numbers

When you round

People I work with often don’t like to round their numbers. It took a lot of effort to get that 317.24

Sometimes they will round their numbers but not enough. “Why can’t I keep a third digit?” they ask. It turns out that the third digit will give you brain pain.

There’s a reason for this. Inside your brain is a spot for short term memory storage. It can usually hold about four pieces of information without a problem. Anything more causes an overload and slows things down.

A pair of two digit numbers will fit into short term memory very easily

In the vet costs example

317 193



When you arrange these numbers

320 190

by placing them within the same row. You could also orient the numbers vertically,

320 190

by placing them in the same column.

Which orientation is best for subtracting?

The vertical orientation appears far more natural for doing a subtraction. Also be sure to place the larger number above the smaller one. If you had the smaller one on top

190 320

it doesn’t work as well.

Try to sort your numbers from high to low. If you have more than one column of numbers

Sorting by one of the columns will do a lot for your data

Have you ever seen a list of numbers for each of the fifty states. It’s almost always alphabetical

Sure you can find your own state quickly

A better approach would be to sort the states by some criteria. List the states with the largest square miles at the top (Alaska

Or list the states with the most people at the top (California

**Costs of pet ownership example

Here is the same table reworked. I rounded each value

^1^includes items like cost of the pet

This table is a lot easier to look at. You might notice a few new patterns that weren’t so obvious before.

You will probably notice other interesting patterns.


If you are displaying numbers


All of the ideas described above were championed by A.S.C. Ehrenberg three decades ago. You can find more details in his book.

A Primer in Data Reduction. A.S.C. Ehrenberg (1982) New York: John Wiley & Sons.

The web site where I got the numbers from is

How Much Does it Cost to Own a Pet?. Steph Bairey. Accessed on 2003-06-04. *“There is plenty of information out there about how to care for and train your pet. However

The numbers on the web page were already rounded

This page was written by Steve Simon while working at Children’s Mercy Hospital. Although I do not hold the copyright for this material

Graphical display](../category/GraphicalDisplay.html). statistics](../category/DescriptiveStatistics.html) or [Category: this one at [Category: Descriptive with general help resources. You can also browse for pages similar to Children’s Mercy Hospital website. Need more information? I have a page reproducing it here as a service