4What makes a good chart? This is from an academic conference paper. What are the problems with this chart?The legend is for how often they find relevant information (given their “following” behavior”)Zhang et al. (2010), “A case study of micro-blogging in the enterprise: use, value, and related issues,” Proceedings of the 28th International Conference on Human Factors in Computing Systems.
5Some basic principles (adapted from Tufte 2009) The chart should tell a story1The chart should have graphical integrity2The chart should minimize graphical complexity3Tufte’s fundamental principle: Above all else show the data
6Principle 1: The chart should tell a story Graphics should be clear on their ownThe depictions should enable meaningful comparisonThe chart should yield insight beyond the text“If the statistics are boring, then you’ve got the wrong numbers.” (Tufte 2009)
9Principle 2: The chart should have graphical integrity Basically, it shouldn’t “lie” (mislead the reader)Tufte’s “Lie Factor”:𝐿𝑖𝑒 𝐹𝑎𝑐𝑡𝑜𝑟= 𝑠𝑖𝑧𝑒 𝑜𝑓 𝑒𝑓𝑓𝑒𝑐𝑡 𝑠ℎ𝑜𝑤𝑛 𝑖𝑛 𝑔𝑟𝑎𝑝ℎ𝑖𝑐 𝑠𝑖𝑧𝑒 𝑜𝑓 𝑒𝑓𝑓𝑒𝑐𝑡 𝑖𝑛 𝑑𝑎𝑡𝑎Should be ~ 1< 1 = understated effect> 1 = exaggerated effect
10Examples of the “lie factor” 𝐿𝐹= 5.3/ /18 = =5.77𝐿𝐹= 4280% (𝑐ℎ𝑎𝑛𝑔𝑒 𝑖𝑛 𝑣𝑜𝑙𝑢𝑚𝑒) 454% (𝑐ℎ𝑎𝑛𝑔𝑒 𝑖𝑛 𝑝𝑟𝑖𝑐𝑒) =9.4Reprinted from Tufte (2009), p. 57 & p. 62
11A more recent, basic example The original graphic from Real Clear Politics, 2008.(Look at the y-axis)The adjusted graphic.
12Other tips to avoid “lying” Adjust for inflationMake sure the context is presentedvs.
13Principle 3: The chart should minimize graphical complexity Generally, the simpler the better…Key conceptsSometimes a table is betterData-inkChartjunk
14When a table is better than a chart For a few data points, a table can do just as well…SalespersonTotal SalesPeacock$225,763.68Leverling$201,196.27Davolio$182,500.09Fuller$162,503.78Callahan$123,032.67King$116,962.99Dodsworth$75,048.04Suyama$72,527.63Buchanan$68,792.25The table carries more information in less space and is more precise.
15The Ultimate Table: The Box Score Large amount of information in a very small spaceSo why does this work?Depends on the reader’s knowledge of the data
16Sales Performance – March 2011 The Business Box Score?Sales Performance – March 2011SalespersonTSWDBDNCDORPeacock2253402028Leverling2012451827Davolio18253822Fuller16216Callahan12311514King1160.512Dodsworth750.310Suyama728Buchanan68Applying the same concept to our salesforce example.How does this help? How could it hurt?Key:TS – total salesWD – worst dayBD – best dayNC – number of customersDOR – days on the road
17Data Ink Should be ~ 1 The amount of “ink” devoted to data in a chart Tufte’s Data-Ink ratio:𝐷𝑎𝑡𝑎−𝑖𝑛𝑘 𝑟𝑎𝑡𝑖𝑜= 𝑑𝑎𝑡𝑎−𝑖𝑛𝑘 𝑡𝑜𝑡𝑎𝑙 𝑖𝑛𝑘 𝑢𝑠𝑒𝑑 𝑖𝑛 𝑔𝑟𝑎𝑝ℎ𝑖𝑐Should be ~ 1< 1 = more non-data related ink in graphic= 1 implies all ink devoted to dataTufte’s principle: Erase ink whenever possible
18Being conscious of data ink Lower data-ink ratio(worse)Higher data-ink ratio(better)
19What makes a good chart? Sometimes it’s really a matter of preference. These both minimize data ink.Why isn’t a table better here?
203-D Charts Evaluate this from a data-ink perspective. How does it affect the clarity of the chart?
21Chartjunk: Data Ink “gone wild” Unnecessary visual clutter that doesn’t provide additional insightDistraction from the story the chart is supposed to conveyWhen the data-ink ratio is low, chartjunk is likely to be high
22Example: Moiré effects (Tufte 2009) Creates illusion of movementStands out, in a bad way
23Example: The Grid Why are these examples of chartjunk? What could you do to remedy it?
24Data Ink Working Against Us Evaluate this chart in terms of Data Ink.Are there better visualizations?
25Data Ink Working For Us Evaluate this chart in terms of Data Ink. Imagine this as a bar chart. As a table!!
26Stacked Bar Charts are Often Trouble Original chart from the BBC websiteWhy is this so difficult to read?What would be a better way to visualize it?
27Key Questions: Can you answer… What are three aspects of a good graphic?How can a chart “lie”?What is the Data Ink ratio and how does it relate to Chartjunk?When is a table better than a chart?