Comparing Graphical Representations of Data

T Brown: M150 Tutorial Discussion Material

"A sentence should contain no unnecessary words, a paragraph no unnecessary sentences for the same reason that a drawing should contain no unnecessary lines and a machine no unnecessary parts." Tufte.

Below are some sets of examples of graphical representations for you to consider and critique and discuss. They have been adapted from a paper by Gary Klass who works in the department of Politics & Government at The Sate University of Illinois. The reference to the website and to his book, “Just Plain Data Analysis: Finding, Presenting, and Interpreting Social Science Data” are below.

Graphics can be poor representations because the information is ambiguous, distorted or distracting. Here are some points to consider for your discussion/critique, can you think of some more?

 Readability o Is the chart appropriate for the purpose? o What is the viewer’s task for the data? o Is there a comparison to be made between different parts of the data? o Are the comparisons obvious? o Can conclusions be drawn spatially or has the data got to be read sequentially and compared?  Improper Labelling o Does the labelling on the graph or chart help the viewer make sense of the data? o Is the labelling clear, detailed and thorough? o Are the axes properly labelled?  Distortion o Does the chart or graph distort in any way what the data has to say? o Are the data ranges in the axis appropriate to represent all the data? o Does the comparison e.g. do the scales on the axes reflect the values and their relationship fairly?  Graphic Overkill/redundant data-ink o Is all the ink data ink – can any be considered redundant, non-data ink so be removed without detracting from the comparisons and conclusions? o Avoiding Chart Junk - Is there any chart junk – context free graphics, cosmetic decoration, or fancy background? T Brown: M150 Tutorial Discussion Material

1) Below are four charts that represent the same data from the Excel spread sheet; which representation works best and why? Which is the most precise? Compare the two pie graphs, probably the best way to represent percentage comparison, which one is for the purpose, explain your conclusion? Why is a graphic representation good for this data?

No in millions % Army 492 35% Navy 381 27% Airforce 363 26% Marines 173 12%

Table: Active Duty Personnel (millions) 1998

2-D Pie Chart 3-D Pie, Exploded

3-D Column Bar Simple 2-D Bar

T Brown: M150 Tutorial Discussion Material

2) Below are two different representations of comparative data, which best represents the comparison, do you consider there is a better alternative representation that should be used?

3) Here is an example of a rather elaborate chart comparing the concentration of income in the industrial Nations (circa 1980) and below a tabular representation of the same data. What is your impression of this chart, does it contain any non-data-ink, is there any redundant information? Can you analyse it spatially or sequentially? T Brown: M150 Tutorial Discussion Material

In the chart above, Kevin Phillips is trying to make the point that income is more inequitably distributed in the United States than in other countries, however a table depicts the data satisfactorily.

Klass comments on the extraneous features of the chart, how did your assessment compare?

 “A completely irrelevant map of the world.  Two entirely different kinds of 3-D charts displayed at two different perspectives.  Country names are repeated three times.  To display 24 numeric data points, 28 numbers are used to define the scales.  The countries are sorted in no apparent order (not even alphabetically).  Note the use of the letter "I" to separate the countries on the bottom chart.” T Brown: M150 Tutorial Discussion Material

4) There are a number of problems with the graph, “Chart 8: Age and Wealth – The New Arithmetic of Poverty”, describe the problems and identify the category that it belongs to.

5) Finally a fourth comparison that demonstrates data distortion. A chart from UNICEF illustrates that the gap between the rich and poor countries in increasing, although the GNP has clearly almost doubled in the wealthiest countries the scale is not designed so that a comparison of growth rate can be made for middle or low income countries. T Brown: M150 Tutorial Discussion Material

Source: World Bank, World Development Indicators 1999, Washington D.C.: World Bank, 1999 (CD-ROM).

Below an example from the same source that seems to distort the data. Note the size of the two arrows, but look carefully at the first arrow, the negative $18 change is represented not by the arrow, but by the little line below it. What is your assessment of the two represenations?

Source: UNICEF, The Progress of Nations 1999; UNDP, Human Development Report 1999 and Human Development Report 1993. T Brown: M150 Tutorial Discussion Material

6) Here is a graph in 3-D that compounds data, bearing in mind that the reproduction is poor, assess its value and success in T Brown: M150 Tutorial Discussion Material

References:

Klass G., (2001), How to Construct Bad Charts and Graphs [online] Laboratory for Integrated Learning and technology, State University of Illinois., Available from: http://lilt.ilstu.edu/gmklass/pos138/datadisplay/badchart.htm [accessed 18th March 2008]

Klass G., (2008) “Just Plain Data Analysis: Finding, Presenting, and Interpreting Social Science Data”, New York: Rowman and Littlefield Publishers, 2008. ISBN: 978-0-7425-6053-6] [online] Available from: http://lilt.ilstu.edu/jpda/ [accessed: 18th March 2008]

Phillips K.,(1991) The Politics of Rich and Poor .Harper Perennial

Tufte E.R., (1993), The Visual Display of Quantitative Information (Cheshire, Conn.: Graphics Press)