1. © 1998, Geoff Kuenning The Art of Graphical Presentation Types of Variables Guidelines for Good Graphics Charts Common Mistakes in Graphics Pictorial Games Special-Purpose Charts

2. © 1998, Geoff Kuenning Types of Variables Qualitative –Ordered (e.g., modem, Ethernet, satellite) –Unordered (e.g., CS, math, literature) Quantitative –Discrete (e.g., number of terminals) –Continuous (e.g., time)

3. © 1998, Geoff Kuenning Charting Based on Variable Types Qualitative variables usually work best with bar charts or Kiviat graphs –If ordered, use bar charts to show order Quantitative variables work well in X-Y graphs –Use points if discrete, lines if continuous –Bar charts sometimes work well for discrete

4. © 1998, Geoff Kuenning Guidelines for Good Graphics Charts Principles of graphical excellence Principles of good graphics Specific hints for specific situations Aesthetics Friendliness

5. © 1998, Geoff Kuenning Principles of Graphical Excellence Graphical excellence is the well- designed presentation of interesting data: –Substance –Statistics –Design

6. © 1998, Geoff Kuenning Graphical Excellence (2) Complex ideas get communicated with: –Clarity –Precision –Efficiency

7. © 1998, Geoff Kuenning Graphical Excellence (3) Viewer gets: –Greatest number of ideas –In the shortest time –With the least ink –In the smallest space

8. © 1998, Geoff Kuenning Graphical Excellence (4) Is nearly always multivariate Requires telling truth about data

9. © 1998, Geoff Kuenning Principles of Good Graphics Above all else show the data Maximize the data-ink ratio Erase non-data ink Erase redundant data ink Revise and edit

10. © 1998, Geoff Kuenning Above All Else Show the Data

11. © 1998, Geoff Kuenning Above All Else Show the Data

12. © 1998, Geoff Kuenning Maximize the Data-Ink Ratio

13. © 1998, Geoff Kuenning Maximize the Data-Ink Ratio

14. © 1998, Geoff Kuenning Erase Non-Data Ink

15. © 1998, Geoff Kuenning Erase Non-Data Ink East West North

16. © 1998, Geoff Kuenning Erase Redundant Data Ink East West North

17. © 1998, Geoff Kuenning Erase Redundant Data Ink East West North

18. © 1998, Geoff Kuenning Revise and Edit

19. © 1998, Geoff Kuenning Revise and Edit

20. © 1998, Geoff Kuenning Revise and Edit

21. © 1998, Geoff Kuenning Revise and Edit

22. © 1998, Geoff Kuenning Revise and Edit

23. © 1998, Geoff Kuenning Revise and Edit

24. © 1998, Geoff Kuenning Revise and Edit

25. © 1998, Geoff Kuenning Specific Things to Do Give information the reader needs Limit complexity and confusion Have a point Show statistics graphically Don’t always use graphics Discuss it in the text

26. © 1998, Geoff Kuenning Give Information the Reader Needs Show informative axes –Use axes to indicate range Label things fully and intelligently Highlight important points on the graph

27. © 1998, Geoff Kuenning Giving Information the Reader Needs

28. © 1998, Geoff Kuenning Giving Information the Reader Needs

29. © 1998, Geoff Kuenning Limit Complexity and Confusion Not too many curves Single scale for all curves No “extra” curves No pointless decoration (“ducks”)

30. © 1998, Geoff Kuenning Limiting Complexity and Confusion

31. © 1998, Geoff Kuenning Limiting Complexity and Confusion

32. © 1998, Geoff Kuenning Have a Point Graphs should add information not otherwise available to reader Don’t plot data just because you collected it Know what you’re trying to show, and make sure the graph shows it

33. © 1998, Geoff Kuenning Having a Point Sales were up 15% this quarter:

34. © 1998, Geoff Kuenning Having a Point

35. © 1998, Geoff Kuenning Having a Point

36. © 1998, Geoff Kuenning Having a Point

37. © 1998, Geoff Kuenning Show Statistics Graphically Put bars in a reasonable order –Geographical –Best to worst –Even alphabetic Make bar widths reflect interval widths –Hard to do with most graphing software Show confidence intervals on the graph –Examples will be shown later

38. © 1998, Geoff Kuenning Don’t Always Use Graphics Tables are best for small sets of numbers –e.g., 20 or fewer Also best for certain arrangements of data –e.g., 10 graphs of 3 points each Sometimes a simple sentence will do Always ask whether the chart is the best way to present the information –And whether it brings out your message

39. © 1998, Geoff Kuenning Text Would Have Been Better

40. © 1998, Geoff Kuenning Discuss It in the Text Figures should be self-explanatory –Many people scan papers, just look at graphs –Good graphs build interest, “hook” readers But text should highlight and aid figures –Tell readers when to look at figures –Point out what figure is telling them –Expand on what figure has to say

41. © 1998, Geoff Kuenning Aesthetics Not everyone is an artist –But figures should be visually pleasing Elegance is found in –Simplicity of design –Complexity of data

42. © 1998, Geoff Kuenning Principles of Aesthetics Use appropriate format and design Use words, numbers, drawings together Reflect balance, proportion, relevant scale Keep detail and complexity accessible Have a story about the data (narrative quality) Do a professional job of drawing Avoid decoration and chartjunk

43. © 1998, Geoff Kuenning Use Appropriate Format and Design Don’t automatically draw a graph –We’ve covered this before Choose graphical format carefully Sometimes a “text graphic” works best –Use text placement to communicate numbers –Very close to being a table

44. © 1998, Geoff Kuenning GNP: +3.8IPG: +5.8CPI: +7.7Profits: +13.3 CEA: +4.7 DR: +4.5 NABE: +4.5 WEF: +4.5 CBO: +4.4 CB: +4.2 IBM: +4.1 CE: +2.9 NABE: +6.2 IBM: +5.9 CB: +5.5 DR: +5.2 WEF: +4.8 IBM: +6.6 NABE: +6.5 CB: +6.2 WEF: +21 DR: +10.5 IBM: +10.4 CE: +6.5 WEF: 6.8 CB: 6.7 NABE: 6.7 IBM: 6.6 DR: 6.5 CBO: 6.3 CEA: 6.3 Unempl: 6.0 About a year ago, eight forecasters were asked for their predictions on some key economic indicators. Here’s how the forecasts stack up against the probable 1978 results (shown in the black panel). (New York Times, Jan. 2, 1979) Using Text as a Graphic

45. © 1998, Geoff Kuenning The Stem-and-Leaf Plot From Tukey, via Tufte, heights of volcanoes in feet: 0|98766562 1|97719630 2|99987766544422211009850 3|876655412099551426 4|9998844331929433361107 5|97666666554422210097731 6|898665441077761065 7|98855431100652108073 8|653322122937

46. © 1998, Geoff Kuenning Choosing a Graphical Format Many options, more being invented all the time –Examples will be given later –See Jain for some commonly useful ones –Tufte shows ways to get creative Choose a format that reflects your data –Or that helps you analyze it yourself

47. © 1998, Geoff Kuenning Use Words, Numbers, Drawings Together Put graphics near or in text that discusses them –Even if you have to murder your word processor Integrate text into graphics Tufte: “Data graphics are paragraphs about data and should be treated as such”

48. © 1998, Geoff Kuenning Reflect Balance, Proportion, Relevant Scale Much of this boils down to “artistic sense” Make sure things are big enough to read –Tiny type is OK only for young people! Keep lines thin –But use heavier lines to indicate important information Keep horizontal larger than vertical –About 50% larger works well

49. © 1998, Geoff Kuenning Poor Balance and Proportion Sales in the North and West districts were steady through all quarters East sales varied widely, significantly outperforming the other districts in the third quarter

50. © 1998, Geoff Kuenning Better Proportion Sales in the North and West districts were steady through all quarters East sales varied widely, significantly outperforming the other districts in the third quarter

51. © 1998, Geoff Kuenning Keep Detail and Complexity Accessible Make your graphics friendly: –Avoid abbreviations and encodings –Run words left-to-right –Explain data with little messages –Label graphic, don’t use elaborate shadings and a complex legend –Avoid red/green distinctions –Use clean, serif fonts in mixed case

52. © 1998, Geoff Kuenning An Unfriendly Graph

53. © 1998, Geoff Kuenning A Friendly Version

54. © 1998, Geoff Kuenning Even Friendlier

55. © 1998, Geoff Kuenning Have a Story About the Data (Narrative Quality) May be difficult in technical papers But think about why you are drawing graph Example: –Performance is controlled by network speed –But it tops out at the high end –And that’s because we hit a CPU bottleneck

56. © 1998, Geoff Kuenning Showing a Story About the Data

57. © 1998, Geoff Kuenning Do a Professional Job of Drawing This is easy with modern tools –But take the time to do it right Align things carefully Check the final version in the format you will use –I.e., print the Postscript one last time before submission –Or look at your slides on the projection screen

58. © 1998, Geoff Kuenning Avoid Decoration and Chartjunk Powerpoint, etc. make chartjunk easy Avoid clip art, automatic backgrounds, etc. Remember: the data is the story –Statistics aren’t boring –Uninterested readers aren’t drawn by cartoons –Interested readers are distracted Does removing it change the message? –If not, leave it out

59. © 1998, Geoff Kuenning Examples of Chartjunk Gridlines! Vibration Pointless Fake 3-D Effects Filled “Floor”Clip Art In or out? Filled “Walls” Borders and Fills Galore Unintentional Heavy or Double Lines Filled Labels

60. © 1998, Geoff Kuenning Common Mistakes in Graphics Excess information Multiple scales Using symbols in place of text Poor scales Using lines incorrectly

61. © 1998, Geoff Kuenning Excess Information Sneaky trick to meet length limits Rules of thumb: –6 curves on line chart –10 bars on bar chart –8 slices on pie chart Extract essence, don’t cram things in

62. © 1998, Geoff Kuenning Way Too Much Information

63. © 1998, Geoff Kuenning What’s Important About That Chart? Times for cp and rcp rise with number of replicas Most other benchmarks are near constant Exactly constant for rm

64. © 1998, Geoff Kuenning The Right Amount of Information

65. © 1998, Geoff Kuenning Multiple Scales Another way to meet length limits Basically, two graphs overlaid on each other Confuses reader (which line goes with which scale?) Misstates relationships –Implies equality of magnitude that doesn’t exist

66. © 1998, Geoff Kuenning Some Especially Bad Multiple Scales

67. © 1998, Geoff Kuenning Using Symbols in Place of Text Graphics should be self-explanatory –Remember that the graphs often draw the reader in So use explanatory text, not symbols This means no Greek letters! –Unless your conference is in Athens...

68. © 1998, Geoff Kuenning It’s All Greek To Me...

69. © 1998, Geoff Kuenning Explanation is Easy

70. © 1998, Geoff Kuenning Poor Scales Plotting programs love non-zero origins –But people are used to zero Fiddle with axis ranges (and logarithms) to get your message across –But don’t lie or cheat Sometimes trimming off high ends makes things clearer –Brings out low-end detail

71. © 1998, Geoff Kuenning Nonzero Origins (Chosen by Microsoft)

72. © 1998, Geoff Kuenning Proper Origins

73. © 1998, Geoff Kuenning A Poor Axis Range

74. © 1998, Geoff Kuenning A Logarithmic Range

75. © 1998, Geoff Kuenning A Truncated Range

76. © 1998, Geoff Kuenning Using Lines Incorrectly Don’t connect points unless interpolation is meaningful Don’t smooth lines that are based on samples –Exception: fitted non-linear curves

77. © 1998, Geoff Kuenning Incorrect Line Usage

78. © 1998, Geoff Kuenning Pictorial Games Non-zero origins and broken scales Double-whammy graphs Omitting confidence intervals Scaling by height, not area Poor histogram cell size

79. © 1998, Geoff Kuenning Non-Zero Origins and Broken Scales People expect (0,0) origins –Subconsciously So non-zero origins are a great way to lie More common than not in popular press Also very common to cheat by omitting part of scale –“Really, Your Honor, I included (0,0)”

80. © 1998, Geoff Kuenning Non-Zero Origins

81. © 1998, Geoff Kuenning The Three-Quarters Rule Highest point should be 3/4 of scale or more

82. © 1998, Geoff Kuenning Double-Whammy Graphs Put two related measures on same graph –One is (almost) function of other Hits reader twice with same information –And thus overstates impact

83. © 1998, Geoff Kuenning Omitting Confidence Intervals Statistical data is inherently fuzzy But means appear precise Giving confidence intervals can make it clear there’s no real difference –So liars and fools leave them out

84. © 1998, Geoff Kuenning Graph Without Confidence Intervals

85. © 1998, Geoff Kuenning Graph With Confidence Intervals

86. © 1998, Geoff Kuenning Confidence Intervals Sample mean value is only an estimate of the true population mean Bounds c 1 and c 2 such that there is a high probability, 1- , that the population mean is in the interval (c 1,c 2 ): Prob{ c 1 <  < c 2 } =1-  where  is the significance level and 100(1-  ) is the confidence level Overlapping confidence intervals is interpreted as “not statistically different”

87. © 1998, Geoff Kuenning Graph With Confidence Intervals

88. © 1998, Geoff Kuenning Scaling by Height Instead of Area Clip art is popular with illustrators: Women in the Workforce 1960 1980

89. © 1998, Geoff Kuenning The Trouble with Height Scaling Previous graph had heights of 2:1 But people perceive areas, not heights –So areas should be what’s proportional to data Tufte defines a lie factor: size of effect in graphic divided by size of effect in data –Not limited to area scaling –But especially insidious there (quadratic effect)

90. © 1998, Geoff Kuenning Scaling by Area Here’s the same graph with 2:1 area: Women in the Workforce 1960 1980

91. © 1998, Geoff Kuenning Poor Histogram Cell Size Picking bucket size is always a problem Prefer 5 or more observations per bucket Choice of bucket size can affect results:

92. © 1998, Geoff Kuenning Principles of Graphics Integrity (Tufte) Proportional representation of numbers Clear, detailed, thorough labeling Show data variation, not design variation Use deflated money units Don’t have more dimensions than data has Don’t quote data out of context

93. © 1998, Geoff Kuenning Proportional Representation of Numbers Maintain a lie factor of 1.0 Use areas, not heights, with clip art Avoiding “decorative” graphs will do wonders –This isn’t too hard for most engineers

94. © 1998, Geoff Kuenning Clear, Detailed, Thorough Labeling Goal is to defeat distortion and ambiguity Write explanations on graphic itself Label important events in the data

95. © 1998, Geoff Kuenning Show Data Variation, Not Design Variation Use one design for the entire graphic In papers, try to use one design for all graphs Again, artistic license is the big culprit

96. © 1998, Geoff Kuenning Use Deflated Money Units Often necessary to show money over time –Even in computer science –E.g., price/performance over time –Or expected future cost of a disk Nominal dollars are meaningless Derate by some standard inflation measure –That’s what the WWW is for!

97. © 1998, Geoff Kuenning Don’t Have More Dimensions Than Data Has This gets back to the Lie Factor 1-D data (e.g., money) should occupy one dimension on the graph: not Clip art is prohibited by this rule –But if you have to, use an area measure $1.00 $2.00

98. © 1998, Geoff Kuenning Don’t Quote Data Out of Context Tufte’s example:

99. © 1998, Geoff Kuenning The Same Data in Context

100. © 1998, Geoff Kuenning Special-Purpose Charts Histograms Scatter plots Gantt charts Kiviat graphs

101. © 1998, Geoff Kuenning Tukey’s Box Plot Shows range, median, quartiles all in one: Tufte can’t resist improvements: or or even minimummaximumquartile median

102. © 1998, Geoff Kuenning Histograms

103. © 1998, Geoff Kuenning Scatter Plots Useful in statistical analysis Also excellent for huge quantities of data –Can show patterns otherwise invisible

104. © 1998, Geoff Kuenning Better Scatter Plots Again, Tufte improves the standard –But it can be a pain with automated tools Can use modified Tukey box plot for axes

105. © 1998, Geoff Kuenning Gantt Charts Shows relative duration of Boolean conditions Arranged to make lines continuous –Each level after first follows FTTF pattern

106. © 1998, Geoff Kuenning Kiviat Graphs Also called “star charts” or “radar plots” Useful for looking at balance between HB and LB metrics

107. © 1998, Geoff Kuenning Useful Reference Works Edward R. Tufte, The Visual Display of Quantitative Information, Graphics Press, Cheshire, Connecticut, 1983. Edward R. Tufte, Envisioning Information, Graphics Press, Cheshire, Connecticut, 1990. Edward R. Tufte, Visual Explanations, Graphics Press, Cheshire, Connecticut, 1997. Darrell Huff, How to Lie With Statistics, W.W. Norton & Co., New York, 1954