Needs and Usability Assessment 11.04.08

I214 Repor ting quantitative data

November 4, 2008

(with thanks to Gary Kass and Edward Tufte)

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…

Needs and Usability Assessment 11.04.08

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

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

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

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

Needs and Usability Assessment 11.04.08

Components of a chart

labelingTitleaxis titles and labelslegendsnotes

scales of X, Y axis

graphicrepresentationsof data

Needs and Usability Assessment 11.04.08

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

Needs and Usability Assessment 11.04.08

Column or bar

Change within smalldata sets that vary overa nominal (ie, category)or interval scale

Column: vertical rectangles

Bar: horizontal

Needs and Usability Assessment 11.04.08

SegmentedcolumnA columnchart thatrepresents thepart-wholerelationshipsof elements

http://www.stanford.edu/group/siqss/research/time_study_files/ProjectReport2005.pdf

Needs and Usability Assessment 11.04.08

Frequency polygon; Histogram

Overall shaperepresentsdistribution ofelements

Needs and Usability Assessment 11.04.08

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

Needs and Usability Assessment 11.04.08

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?

Needs and Usability Assessment 11.04.08

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

Needs and Usability Assessment 11.04.08

Analysis

Looking for significantdifferences acrossimportant groups

Looking for correlation– inferring causality

Polls includingmobile phones

Needs and Usability Assessment 11.04.08

Maps

Placingdata onphysicalspace

Needs and Usability Assessment 11.04.08

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

Needs and Usability Assessment 11.04.08

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?

Needs and Usability Assessment 11.04.08

Reporting: last words

Graphics are visualmetaphors.They are rhetoric.

Do you know the storyyou want to tell?

…the story youraudience is seeing?

Needs and Usability Assessment 11.04.08

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