1. January 20071R. Smith - qmcs 200 QMCS 200 Types of Charts Graphical Integrity

2. January 20072R. Smith - qmcs 200 Today’s Class Review last TIA homeworkReview last TIA homework Review ExamReview Exam Finish up the first exerciseFinish up the first exercise Talk about Network LabTalk about Network Lab Talk about multi-series chartsTalk about multi-series charts Talk about graphical integrityTalk about graphical integrity Chapter 2, HOE #2Chapter 2, HOE #2

3. January 20073R. Smith - qmcs 200 Using Charts: What are we doing? One series or many?One series or many? –1 series: it’s easy – stacked and clustered are identical! –Multiple: decide between cluster, stacked, 100% stacked Looking at absolute or relative values?Looking at absolute or relative values? –Relative numbers: Pie or 100% Stacked Chart –Absolute numbers: Column, Area, Bar, Line, etc. Categories, or some sort of sequence?Categories, or some sort of sequence? –Categories = Column or Bar Chart –Sequence = Line or Area Chart Comparing category totals or subtotals?Comparing category totals or subtotals? –Totals = Stacked Chart –Subtotals = Cluster Chart

4. January 20074R. Smith - qmcs 200 Handling multiple series Graph the data only, not the totals!Graph the data only, not the totals! –This throws off the whole appearance of your graph –In a stacked chart, it makes the chart unreadable Pick the right axis for the chartPick the right axis for the chart –What clusters or stacked totals do you want to compare?

5. January 20075R. Smith - qmcs 200 Building Good Graphics Some ideas regarding quality graphics Graphical IntegrityGraphical Integrity –A graphic’s most obvious interpretations must be consistent with the underlying data –Avoid accidental or intentional misrepresentation Forgo “chartjunk” that draws attention away from the dataForgo “chartjunk” that draws attention away from the data –Examples: moiré vibration, grids, graphical “ducks” Maximize the Data-to-Ink ratioMaximize the Data-to-Ink ratio –Data-to-Ink Ratio = ink used to print the actual data all ink used to print the graphic

6. January 20076R. Smith - qmcs 200 The “Lie Factor” – an example New York Times, August 9, 1978New York Times, August 9, 1978

7. January 20077R. Smith - qmcs 200 The Lie Factor Computes the effect of distortion in a quantitative graphic like a chartComputes the effect of distortion in a quantitative graphic like a chart Lie Factor = size effect shown in graphic size effect in the dataLie Factor = size effect shown in graphic size effect in the data More than 5% (.95 to 1.05) is substantialMore than 5% (.95 to 1.05) is substantial –Not caused by errors in drafting Lie Factors of 2 to 5 are commonLie Factors of 2 to 5 are common

8. January 20078R. Smith - qmcs 200 Calculating the Lie Factor Change in fuel economy from 1978-1985 = 53% (0.53)Change in fuel economy from 1978-1985 = 53% (0.53) Change in graphic = change from 0.6” to 5.3”Change in graphic = change from 0.6” to 5.3” (5.3 - 0.6)/0.6 = 7.83 = 783%(5.3 - 0.6)/0.6 = 7.83 = 783% Lie Factor = 7.83/0.53 = 14.8 -- almost 15 times realityLie Factor = 7.83/0.53 = 14.8 -- almost 15 times reality

9. January 20079R. Smith - qmcs 200 An Accurate View Accurate in 2 dimensionsAccurate in 2 dimensions Puts numbers in context by including current and expected average MPG of cars on the roadPuts numbers in context by including current and expected average MPG of cars on the road

10. January 200710R. Smith - qmcs 200 Good Graphics and Excel It’s hard to build an inaccurate graph, unless you make a mistakeIt’s hard to build an inaccurate graph, unless you make a mistake –Including totals, swapping the axes by mistake, etc. It’s easy to build a “visually busy” graphIt’s easy to build a “visually busy” graph –Excel “guesses” about colors –You have to adjust things to work with your printing environment It’s easy to crank up the data-to-ink ratioIt’s easy to crank up the data-to-ink ratio –3D graphs are mostly wasted ink –3D graphs can be misleading, too

11. January 200711R. Smith - qmcs 200 Possible Distortions in Excel Data Problems (GIGO)Data Problems (GIGO) –Ignoring monetary inflation –Comparing time periods of different durations –Omitting data that provides context –Ignoring other factors that differ in the categories Visual ProblemsVisual Problems –Data-to-Ink Ratio – Excel uses lots of ink and color even when not needed –3D graphics – can visually misrepresent relative values

12. January 200712R. Smith - qmcs 200 Examples The mis-scaled gas mileageThe mis-scaled gas mileage Oil Prices and InflationOil Prices and Inflation Nobel Prizes and time periodsNobel Prizes and time periods Context and traffic enforcementContext and traffic enforcement Influences on state budgetsInfluences on state budgets 2D and 3D ambiguities2D and 3D ambiguities

13. January 200713R. Smith - qmcs 200 Oil Prices and Inflation

14. January 200714R. Smith - qmcs 200 Inconsistent Time Periods National Science Foundation, 1974National Science Foundation, 1974

15. January 200715R. Smith - qmcs 200 Inconsistent Time Periods National Science Foundation, 1974National Science Foundation, 1974

16. January 200716R. Smith - qmcs 200 Context is Essential Two data points can’t possibly tell the story aloneTwo data points can’t possibly tell the story alone

17. January 200717R. Smith - qmcs 200 So, what’s the real story? Different contexts yield different interpretationsDifferent contexts yield different interpretations Is this a blip, or a real change, or part of a cycle?Is this a blip, or a real change, or part of a cycle?

18. January 200718R. Smith - qmcs 200 Connecticut Statistics Actually, drop was a return to previous levelsActually, drop was a return to previous levels “Why did deaths go up 1954-56?”“Why did deaths go up 1954-56?”

19. January 200719R. Smith - qmcs 200 Regional Statistics Compare per capita deaths in region over nearby yearsCompare per capita deaths in region over nearby years All states enjoyed a reduction, not just the state that cracked downAll states enjoyed a reduction, not just the state that cracked down

20. January 200720R. Smith - qmcs 200 Budget Inflation Revisited New York State budgets and aid to municipalitiesNew York State budgets and aid to municipalities Dramatic growth, right?Dramatic growth, right?

21. January 200721R. Smith - qmcs 200 Visual Trickery Material on left, and perspective on early years make them appear smallMaterial on left, and perspective on early years make them appear small Horizontal arrows emphasize small sizeHorizontal arrows emphasize small size Perspective makes the rightmost cluster stand forward, looking extra largePerspective makes the rightmost cluster stand forward, looking extra large Vertical arrows emphasize heightVertical arrows emphasize height

22. January 200722R. Smith - qmcs 200 Reducing Data-to-Ink Ratio If we take out the extra graphics and perspective (left) we yield a simple story (right)If we take out the extra graphics and perspective (left) we yield a simple story (right) But the story is still misleadingBut the story is still misleading

23. January 200723R. Smith - qmcs 200 Adjusting for Change Take into account both inflation and population changeTake into account both inflation and population change This story shows no significant changes in 7 yearsThis story shows no significant changes in 7 years

24. January 200724R. Smith - qmcs 200 A 2-D Graphics Problem Washington Post, October 25, 1978Washington Post, October 25, 1978 Inflation is one-dimensionalInflation is one-dimensional Shrinking money in 2 dimensions is misleadingShrinking money in 2 dimensions is misleading Dollar’s area should reflect its purchasing powerDollar’s area should reflect its purchasing power The 1978 dollar should be about twice as large as shownThe 1978 dollar should be about twice as large as shown

25. January 200725R. Smith - qmcs 200 A 3-D Graphics Problem Problem with 3D imageProblem with 3D image Prices increased 454%Prices increased 454% Graphic size: 4,280%Graphic size: 4,280% Lie Factor = 9.4Lie Factor = 9.4 –If we take the “barrel metaphor” seriously, the barrel volume increases 27,000% –Lie Factor = 59.4

26. January 200726R. Smith - qmcs 200 Excel 3D Pie Chart Gives Denver (19%) more ink than Miami (21%)Gives Denver (19%) more ink than Miami (21%) Makes Boston look overwhelmingMakes Boston look overwhelming Makes New York look much less pitifulMakes New York look much less pitiful

27. January 200727R. Smith - qmcs 200 Minimizing Data to Ink Ratio How much ink do you really need to display the data you have?How much ink do you really need to display the data you have? Extra ink is chartjunkExtra ink is chartjunk –Makes the chart feel like it says more that it really does A checklistA checklist –Extra “dimensions” like 3D blocks in a 2D bar chart –Shaded backgrounds – do they make the data easier to see, or do they waste ink? –Grid lines – do they really help people compare the data?

28. January 200728R. Smith - qmcs 200 For More Information Edward Tufte’s The Visual Display of Quantitative InformationEdward Tufte’s The Visual Display of Quantitative Information Chapter 2: “Graphical Integrity”Chapter 2: “Graphical Integrity” –Also, notes from other chapters www.edwardtufte.comwww.edwardtufte.com