Seeing something onceis worth hearing about it

a hundred times.

The Solution:

The double y-axis graph

The most powerful tool for misleading graphics ever

devised.

I gather, young man, that you wish to be a Member of Parliament. The first lesson that you must learn is, when I call for statistics about the rate of

infant mortality, what I want is proof that fewer babies died when I was Prime Minister than when anyone else was Prime Minister. That is a

political statistic.

Winston Churchill (1874-1965)

The Ithaca Times - October 20, 2000

How to display data badly

Howard WainerNational Board of Medical Examiners

Three wonderful books by my favorite author:

Picturing the Uncertain World: How to Understand, Communicate and Control Uncertainty through Graphical Display . Princeton, NJ: Princeton University Press,

2009.

Graphic Discovery: A Trout in the Milk and Other Visual Adventures. Princeton, N.J.: Princeton University

Press, 2005.

Visual Revelations: Graphical Tales of Fate and Deception from Napoleon Bonaparte to Ross Perot. (2nd edition) Hillsdale, N. J.: Lawrence Erlbaum Associates,

2000.

“Closing averages on the human scene were mixed today.Brotherly love was down two points,

while enlightened self-interest gained a half.Vanity showed no movement, and

guarded optimism slipped a point in sluggish trading.Overall, the status quo remained unchanged.”

Of good graphs it may be said what Mark Van Doren observed about brilliant conversationalists:

In their presence others speak well.

A good graph is quiet and lets the data tell their story clearly and

completely.

Along each line are numbers which are turning points in the race between men and fire,

And if the lines are viewed as a race the numbers mark off legs of the race,

If they also have religious significance they are stations of the cross,

And if they have literary significance they mark off acts of drama,…

But the acts are short, because modern wildfire allows no time for soliloquies.

Norman Maclean (1992) Young Men and Fire. Chicago: University of Chicago Press.

The four purposes of graphs

1. Exploration - The data contain a message and we would like to find out what it is.

2. Communication - We know something and we wold like to tell others.

3. Calculation - Graphs can serve as visual algorithms (nomogaphs) that enable us to determine at-a-glance what might otherwise be tedious to calculate.

4. Decoration - Graphs are pretty and can be used to enliven what might otherwise be a dull presentation.

“Some, to beautify their Halls, Parlors,

Chambers, Galeries, Studies, or Libraries….

Liketh, loveth, getteth and useth, Maps,

Charts, and Geographicall Globes.”

(John Dee, 1570)

The Aim of Good Data Graphics

is toDisplay Data

Accurately and Clearly.

I. Include as few data as possible

(minimize the data density)

You can boost data density through the use of small multiples

II. Hide what data you do show

(minimize the data-ink ratio)

Hide the data in the grid

Relation of Actual Rates of Registration to Predicted Rates (104 cities 1960)

Another published version of the same data improved the data-ink ratio up to about 0.7.

Hide the data in the scale

III. Ignore the Visual Metaphor

Show the Data Accurately

The OldGoosing up the effect

BySquaring the Eye-Ball

Trick

IV. Only Order Matters(maximize the lie factor)

V. Graph Data out of Context

Show the Data Clearly

VI. Change Scales in Mid-Axis

VII. Emphasize the Trivial

(Ignore the Important)

VIII. Jiggle the Baseline

IX. Alabama First

Even the best of graphics can sometimes use a little explanation

X. Label: Illegibly,Incompletely,

Incorrectly, Ambiguously

“Everyone spoke of an information overload,

but what there was, in fact, was a non-information overload.”

(Wurman, 1976)

XI. More is Murkier:More Decimal PlacesMore Dimensions

Economists state their GNP growth

projections to the nearest tenth of a percentage point to prove they have a sense of humor.

Edgar R. Fiedler

An example fromState Court Caseload Statistics:

1976

Ln(DIAC) = -.10729131 + 1.00716993 x Ln(FIAC)

Where DIAC = Number of DispositionsFIAC = Number of Filings

with eight digits shown it implies a standard error of

.000000005or

n ~ 4 x 1016

The actual n (the number of states) allows one digit of

accuracy at most.Or

DIAC = .9 FIACor

“There are about 90% as many dispositions as filings.”

My colleague Al Biderman, who knows more about state courts

than I do, said it needs yet one more digit of rounding, or

There are about as many dispositions as filings.

The worst graph ever to

find its way into print.

American Education

A Graphical Duck

from the Bureau of the Census

XII. If it has been done well in the past, think of a new

way to do it.

The World’s Champion Graph

Designed and drawn by Charles Joseph Minard

November 20, 1869