of Principles Graphical Display
Tables and Graphs
Meaningful data Unambiguous data Efficient display
Meaningful Data
Make Meaningful Comparisons
Rates, ratios Before and after Cross sectional, between groups Time series Adjust for inflation
Unambiguous
Define data with titles, legends, labels, footnotes. Specify the source
Table 4: Change in Teenage Birth Rates: 19871998 White Black Asian Hispanic 6.7% -4.9 -1.8 3.7
Source: Statistical Abstract 2000, Table 85
Efficient:
Minimize the inktodata ratio Sort data on meaningful variable (not alphabetical) Use consistent formatting across tables
Ink to data ratio
Deemphasize gridlines, borders and backgrounds Never use 3D Display more than 1 variable Use data labels, not scales to minimize the number of numbers
Proper sorting
Time goes left to right Highlight comparisons
Avoid Distortion
Beware of scaling effects Use tables if variables are of different units: e.g., dollars and percents. Adjust variables in common units to common starting point Use right and left scales
Figure 7: Scaling distortion
Pies are bad
note how the 3D pie exaggerates the relative size of the front slice
2D is better than 3D, but.....
Bars provide better a visual image of relative size than pie slices
"How would you rate President Bush's performance on the job?"
(% excellent or good) 90 80 70 60 50 40 30
Jan-01 Dec-03 Dec-01 Jun-04 Jul-01 Dec-04 Jun-03 Dec-02 Dec-05 Jun-06 Jun-05 Jul-02 9/11
"Major combat operations in Iraq have ended" election Hurricane Katrina
source: Zogby International, "George W. Bush - Job Performance Rating," (Zogby special feature) http://www.zogby.com/features/zogbytables4.cfm
George W. Bush: Job Approval and Unemployment Rates
90 80 9 8 7 6
unemployment
Job Approval
70 60 50 job approval 40 30
Jan-01 Jul-02 Dec-01 Dec-02 Jun-03 Dec-05 Dec-03 Dec-04 Jun-05 Jul-01 Jun-04
5 4 3
Jun-06
source: Zogby International, "George W. Bush - Job Performance Rating," (Zogby special feature) http://www.zogby.com/features/zogbytables4.cfm unemployment: Bureau of Labor Statistics
Unemployment rate
State Math Scores and Students' TV Viewing Habits
290 1992 State 8th-grade NAEP Math Score
MN ND IA WI ME NH NE ID MA COWYPA IN
280
UT
CT MI NJ
270 260 250 240
MO OKOH TX NY VA MD RI AZ NC DE KY WV CANM TN FL SC GA
AR AL LA MS
HI
DC
230
0
5
10
15
20
25
30
% Students watching TV 6 hrs+ per day
source: National Center for Educational Statistics, 1994