214 reporting quantitative data - uc berkeley school of...
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Needs and Usability Assessment 11.04.08
I214 Repor ting quantitative data
November 4, 2008
(with thanks to Gary Kass and Edward Tufte)
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Needs and Usability Assessment 11.04.08
Why graphs?
Ex: The Harris Poll #100, Oct 15, 2007
American adults have their choice of many differentcuisines … From pasta to burritos, the choices are almostendless. But what do Americans choose when eating out?American food, of course!
Over one-quarter (28%) of U.S. adults say A merican food is what theyare most l ikely to choose i f they had the choice to go out to arestaurant and eat one type of food. Just under one-quarter (22%) saythat they would most l ikely choose Ital ian while 17 percent wouldchoose Mexican while 16 percent would choose Chinese i f they had thechoice to go out to a restaurant. Japanese is the next choice as sevenpercent say they would choose this type of cu isine. Much furtherdown the l ist are Indian (2% say they would choose) and then Frenchand Middle Eastern cu isine (1% would choose each). Final ly , fourpercent say they would choose another type of food.
or…
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Needs and Usability Assessment 11.04.08
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Needs and Usability Assessment 11.04.08
Reporting results the easy way
SE9. How confident do you feel about your own searching abilitieswhen using a search engine to find information online?
Based on Internet users who have a used a search engine[N=1,165]% 48 Very confident 44 Somewhat confident 6 Not too confident 2 Not confident at all * Don’t know/Refused
http://www.pewinternet.org/pdfs/PIP_Search_Questions.pdf
exact questions and answers
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Needs and Usability Assessment 11.04.08
Tabular displays
n= 12n = 10n = 2No ans.
100n = 308
100n = 190
100n = 118Total
69N=127
87N=165
40N=47Dissatisfied
31N=96
13N=25
60N=71Satisfied
Total%n=320
Grads%n=200
Undergrads%n=120
Comparing dependent to independent variables
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Needs and Usability Assessment 11.04.08
Good information graphics
Efficientminimizing non-data ink
Meaningfuldisplaying informationrelevant to theargument
UnambiguousSelf-explanatory, or atleast difficult tomisread
http://www.prb.org/Artic les/2007/623Urbanization.aspx
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Needs and Usability Assessment 11.04.08
5 principlesfrom E. Tufte
Visual Display of Quantitative Information,p 103 and 105
Above all else show the data
Maximize the data-ink ratio
Erase non-data-ink, within reason
Erase redundant data-ink
Revise and edit
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Components of a chart
labelingTitleaxis titles and labelslegendsnotes
scales of X, Y axis
graphicrepresentationsof data
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Area chart
How the dependentrelationship of parts ofa whole varies over anindependent variable
Percentage: sum of the twoalways represents 100%
Cumulative: sum variesaccording to elements
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Column or bar
Change within smalldata sets that vary overa nominal (ie, category)or interval scale
Column: vertical rectangles
Bar: horizontal
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SegmentedcolumnA columnchart thatrepresents thepart-wholerelationshipsof elements
http://www.stanford.edu/group/siqss/research/time_study_files/ProjectReport2005.pdf
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Frequency polygon; Histogram
Overall shaperepresentsdistribution ofelements
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Line charts
Used to interpolate betweendata points and extrapolatefuture valuesTrends or change over timeLooking for correlationsbetween variables
Lines: Connect "real" data points
Curves: represent functionalrelations between data points orto interpolate data
X must have numerical values!
http://www.fivethirtyeight.com/2008/11/google-traffic-suggests-mccain-not.html
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Pie chart
Good for displayingapproximate percentagesat a single point in time
Caution:Makes exact comparisonsdifficult
You cannot necessarilycompare pie charts to each other
Maybe use a bar chart instead?
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Scatterplot
One dimensionalShow measurements over time
Two-dimensionalConvey an overall impression ofthe relation between two variables
Some caution:Not good for following trends
Should not be used with morethan one independent variable
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Analysis
Looking for significantdifferences acrossimportant groups
Looking for correlation– inferring causality
Polls includingmobile phones
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Maps
Placingdata onphysicalspace
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Representing change withsmall multiples
Smallmultiples
“Graphicaldepictions of
variableinformation
that sharecontext, but not
content.”Edward Tufte
Tufte, E. Envisioning Information. Cheshire, CT: Graphics Press (1990).
graphic: www.uxmatters.com/MT/archives/000044.php
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Reportingguidelines
The readershould be ableto reconstructwhat you did
Show thequestion
Include all dataie, percentagesand numbers ofrespondents
n= 12n = 10n = 2No ans.
100n = 308
100n = 190
100n = 118Total
69N=127
87N=165
40N=47Dissatisfied
31N=96
13N=25
60N=71Satisfied
Total%n=320
Grads%n=200
Undergrads%n=120
Table 1: Opinion on foodAre you satisfied or disssatisfied with the bagels at the FreeSpeech Movement Café?
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Reporting: last words
Graphics are visualmetaphors.They are rhetoric.
Do you know the storyyou want to tell?
…the story youraudience is seeing?
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Appendix A:Good places to look for examplereportsPew Internethttp://www.pewinternet.org/pdfs/PIP_Searchengine_users.pdf pp. i-
ivhttp://www.pewinternet.org/pdfs/PIP_Future_of_Internet_2006.pdfhttp://www.pewinternet.org/pdfs/PIP_Search_Questions.pdf"What Do Americans Do on the Internet?“ Appendix B
Harris Interactive Pollhttp://www.harrisinteractive.com/harris_poll/
Stanford Time Studyhttp://www.stanford.edu/group/siqss/SIQSS_Time_Study_04.pdf