QMCS 200

January 2007 1R. Smith - qmcs 200

QMCS 200QMCS 200

Types of ChartsTypes of Charts

Graphical IntegrityGraphical Integrity


Today’s ClassToday’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


Using Charts: What are we doing?Using Charts: What are we doing?

• One series or many?One series or many?– 1 series: it’s easy – stacked and clustered are identical!1 series: it’s easy – stacked and clustered are identical!– Multiple: decide between cluster, stacked, 100% stackedMultiple: decide between cluster, stacked, 100% stacked

• Looking at absolute or relative values?Looking at absolute or relative values?– Relative numbers: Pie or 100% Stacked ChartRelative numbers: Pie or 100% Stacked Chart– Absolute numbers: Column, Area, Bar, Line, etc.Absolute numbers: Column, Area, Bar, Line, etc.

• Categories, or some sort of sequence?Categories, or some sort of sequence?– Categories = Column or Bar ChartCategories = Column or Bar Chart– Sequence = Line or Area ChartSequence = Line or Area Chart

• Comparing category Comparing category totalstotals or or subtotalssubtotals??– Totals = Stacked ChartTotals = Stacked Chart– Subtotals = Cluster ChartSubtotals = Cluster Chart


Handling multiple seriesHandling multiple series

• Graph the Graph the datadata onlyonly, not the , not the totalstotals!!– This throws off the whole appearance of your graphThis throws off the whole appearance of your graph– In a stacked chart, it makes the chart unreadableIn 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?What clusters or stacked totals do you want to compare?


Building Good GraphicsBuilding Good Graphics

Some ideas regarding quality graphicsSome ideas regarding quality graphics• Graphical IntegrityGraphical Integrity

– A graphic’s most obvious interpretations must be consistent A graphic’s most obvious interpretations must be consistent with the underlying datawith the underlying data

– Avoid accidental or intentional misrepresentationAvoid accidental or intentional misrepresentation

• Forgo “chartjunk” that draws attention away Forgo “chartjunk” that draws attention away from the datafrom the data– Examples: moirExamples: moiré vibration, grids, graphical “ducks”é vibration, grids, graphical “ducks”

• Maximize the Data-to-Ink ratioMaximize the Data-to-Ink ratio– Data-to-Ink Ratio = Data-to-Ink Ratio = ink used to print the actual dataink used to print the actual data

all ink used to print the graphic all ink used to print the graphic


The “Lie Factor” – an exampleThe “Lie Factor” – an example

• New York Times, August 9, 1978New York Times, August 9, 1978


The Lie FactorThe Lie Factor

• Computes the effect of distortion in a Computes the effect of distortion in a quantitative graphic like a chartquantitative graphic like a chart

• Lie Factor = Lie Factor = size effect shown in graphicsize effect shown in graphic size effect in the data 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 draftingNot caused by errors in drafting

• Lie Factors of 2 to 5 are commonLie Factors of 2 to 5 are common


Calculating the Lie FactorCalculating 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


An Accurate ViewAn Accurate View

• Accurate in 2 Accurate in 2 dimensionsdimensions

• Puts numbers in Puts numbers in context by context by including current including current and expected and expected average MPG of average MPG of cars on the roadcars on the road


Good Graphics and ExcelGood Graphics and Excel

• It’s hard to build an inaccurate graph, unless It’s hard to build an inaccurate graph, unless you make a mistakeyou make a mistake– Including totals, swapping the axes by mistake, etc.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 colorsExcel “guesses” about colors– You have to adjust things to work with your printing You have to adjust things to work with your printing

environmentenvironment

• 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 ink3D graphs are mostly wasted ink– 3D graphs can be misleading, too3D graphs can be misleading, too


Possible Distortions in ExcelPossible Distortions in Excel

• Data Problems (GIGO)Data Problems (GIGO)– Ignoring monetary inflationIgnoring monetary inflation– Comparing time periods of different durationsComparing time periods of different durations– Omitting data that provides contextOmitting data that provides context– Ignoring other factors that differ in the categoriesIgnoring other factors that differ in the categories

• Visual ProblemsVisual Problems– Data-to-Ink Ratio – Excel uses lots of ink and color even when Data-to-Ink Ratio – Excel uses lots of ink and color even when

not needednot needed– 3D graphics – can visually misrepresent relative values3D graphics – can visually misrepresent relative values


ExamplesExamples

• 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


Oil Prices and InflationOil Prices and Inflation


Inconsistent Time PeriodsInconsistent Time Periods

• National Science Foundation, 1974National Science Foundation, 1974


Context is EssentialContext is Essential

• Two data points can’t possibly tell the story aloneTwo data points can’t possibly tell the story alone


So, what’s the real story?So, what’s the real story?

• Different contexts yield Different contexts yield different interpretationsdifferent interpretations

• Is this a blip, or a real Is this a blip, or a real change, or part of a cycle?change, or part of a cycle?


Connecticut StatisticsConnecticut 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?”


Regional StatisticsRegional Statistics

• Compare per capita Compare per capita deaths in region over deaths in region over nearby yearsnearby years

• All states enjoyed a All states enjoyed a reduction, not just the reduction, not just the state that cracked downstate that cracked down


Budget Inflation RevisitedBudget Inflation Revisited

• New York State budgets and aid to municipalitiesNew York State budgets and aid to municipalities• Dramatic growth, right?Dramatic growth, right?


Visual TrickeryVisual Trickery

• Material on left, and Material on left, and perspective on early perspective on early years make them years make them appear smallappear small

• Horizontal arrows Horizontal arrows emphasize small sizeemphasize small size

• Perspective makes Perspective makes the rightmost cluster the rightmost cluster stand forward, stand forward, looking extra largelooking extra large

• Vertical arrows Vertical arrows emphasize heightemphasize height


Reducing Data-to-Ink RatioReducing Data-to-Ink Ratio

• If we take out the extra graphics and If we take out the extra graphics and perspective (left) we yield a simple story (right)perspective (left) we yield a simple story (right)

• But the story is still misleadingBut the story is still misleading


Adjusting for ChangeAdjusting for Change

• Take into account both Take into account both inflationinflation and and population changepopulation change• This story shows no significant changes in 7 yearsThis story shows no significant changes in 7 years


A 2-D Graphics ProblemA 2-D Graphics Problem

• Washington Post, October 25, Washington Post, October 25, 19781978

• Inflation is one-dimensionalInflation is one-dimensional• Shrinking money in 2 Shrinking money in 2

dimensions is misleadingdimensions is misleading• Dollar’s Dollar’s areaarea should reflect its should reflect its

purchasing powerpurchasing power• The 1978 dollar should be The 1978 dollar should be

about twice as large as shownabout twice as large as shown


A 3-D Graphics ProblemA 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 If we take the “barrel metaphor” seriously, the metaphor” seriously, the barrel barrel volumevolume increases increases 27,000%27,000%

– Lie Factor = 59.4Lie Factor = 59.4


Excel 3D Pie ChartExcel 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


Minimizing Data to Ink RatioMinimizing Data to Ink Ratio

• How much ink do you How much ink do you reallyreally need to display the need to display the data you have?data you have?

• Extra ink is chartjunkExtra ink is chartjunk– Makes the chart feel like it says more that it really doesMakes the chart feel like it says more that it really does

• A checklistA checklist– Extra “dimensions” like 3D blocks in a 2D bar chartExtra “dimensions” like 3D blocks in a 2D bar chart– Shaded backgrounds – do they make the data easier to see, or Shaded backgrounds – do they make the data easier to see, or

do they waste ink?do they waste ink?– Grid lines – do they really help people compare the data?Grid lines – do they really help people compare the data?


For More InformationFor More Information

• Edward Tufte’s Edward Tufte’s The Visual The Visual Display of Quantitative Display of Quantitative InformationInformation

• Chapter 2: “Graphical Chapter 2: “Graphical Integrity”Integrity”– Also, notes from other chaptersAlso, notes from other chapters

• www.edwardtufte.comwww.edwardtufte.com

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