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The Visual Display of Quantitative Information

By TLF Research

If a picture is worth a thousand words, how many should a chart be worth? A good one can summarise thousands of data points and highlight a causal relationship; poor ones can obscure a few simple numbers with meaningless “chartjunk”, adding nothing but confusion and irritation. The Visual Display of Quantitative Information, one of Amazon’s books of the century, is essential reading for designers, analysts, and managers who want to produce better graphs.

Rescuing data graphics from the artists

When most people think of graphing statistics, if they think of it at all, what comes to mind is probably How to Lie With Statistics. But the problem is far deeper than deliberate deceit. The use of data graphics as a gimmick to hold the attention of readers assumed to be too dull-witted to understand numbers has led to a triumph of style (or fluff) over substance. Too many graphics are either patronisingly simplistic, drowning in decoration or downright misleading. Edward Tufte is on a mission to set that right, starting with a couple of rules:

  • If the statistics are boring then you’ve got the wrong numbers
  • You should respect the intelligence of your audience Most bad graphics don’t set out to mislead.

For example any graph purporting to show a change in price that charts actual as opposed to “real” cost is always misleading, even though it reflects the original numbers perfectly well. Accurate graphing takes thought and experience as well as integrity, which is why it should be a task for those who can combine an aesthetic touch with some statistical and analytical expertise. Tufte has a knack for firing the enthusiasm of those who read his work. His style is witty and engaging, occasionally becoming acerbic when discussing a particularly bad example. Of one truly monstrous 3D graphic from the pages of American Education he comments: “five colors report, almost by happenstance, only five pieces of data....This may well be the worst graphic ever to find its way into print.” It certainly is hideous, but dating from the 1970s it seems in retrospect only a warning of what was to come with the advent of desktop computing and Chart Wizards.

Playfair Bar chart

The good, the bad and the ugly

Tufte raids his considerable library of rare books to illustrate good and bad design.

Tufte on PowerPoint

The reminder that ideas such as the bar chart, time series and scatter plot were inventions rather than solutions handeddown from on high is a salutary one that should prompt us to ask if things can be made better. The example above may be the first bar chart? Playfair was unconvinced, but the idea has stood the test of time The choice of graph really does matter. Before the scatter plot how was it possible to examine the relationship between two variables? Fundamentally it wasn’t. The use of the right chart could make a significant difference to your analysis, particularly with complex multivariate data. Tufte provides examples of good practice ranging from Galileo to 3D computervisualisations, some of which are truly inspirational. It is revealing that the very best data graphics are often one-offs; works of art that bring to life a specific set of data. Minard’s 1869 map above narrates Napoleon’s disastrous 1812 campaign:

Figurative Map

Combining chart, map and time-series it chronicles the terrible losses of the French army in the diminishing width of the line showing advance and retreat. According to Tufte it “may well be the best statistical graphic ever drawn.” It certainly has a stark power that would be difficult to match in words. Tufte does not just lay down principles and show examples of good and bad practice. Perhaps the most useful sections of the book are those in which he elaborates some of his ideas for redesigning standard graphs step by step. This takes the work from the realm of theory to practical application, and some of his suggestions are enormously valuable, deserving wide adoption. His latest innovation, the sparkline (to be featured in the forthcoming Beautiful Evidence) is already gathering considerable momentum, and may be the first of his suggestions to reach the mainstream.

Sparklines

His main aim in making changes is to maximise the “data-ink ratio”. Any mark on the paper should add to the information contained, if it does not then it can be erased. A good example is the overbearing grid that dominates so many charts. Sometimes a light grid may help when looking up specific data, but a heavy grid just gets in the way.

Biography

Effective graphing

Charts that explain

Tufte points out that the best charts are those which reveal something that could not easily be seen in the data alone. Simple data are often best shown in the most simple way - a table. Pie charts, by this rationale, are rarely a good use of ink. Of course tables present a typographic challenge that is worthy of a book in itself, and are often just as poorly produced as the average graph! The point is that numbers can best be made interesting not by turning them into asinine pictures, but by facilitating comparisons and highlighting relationships. Simple tables and pie charts don’t do this well, but intelligently designed tables, time series and multivariate data plots are all capable of revealing new and interesting truths. A good measure of graphical excellence is data density, almost precisely a measure of how many words the chart is worth. If the data density is lower than a table, then the chances are a table would be better.

Does it really matter?

Perhaps you’re thinking that this is a diatribe that we can afford to dismiss. The way data is presented surely can’t make all that much difference? I would argue that it is hard to overestimate the importance of this area. The point is that bad graphics can not only be made to lie, but frequently mislead or hide information inadvertently because of poor design, and this has daily consequences for the decisions we make. Is the way you present data really important? Yes, if you’re talking about data on cancer death rates. Yes, if you’re talking about the key information relating to the safety of a NASA shuttle mission. Yes, if you’re talking about any data that matters at all. And if doesn’t, then why are you graphing it in the first place?

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