Chapter 7 Page 1 of 7
Chapter 7
Misleading Graphs
Spring 2016 1/9/16
Learning Objectives:
Chapter 7 Page 2 of 7
Chapter 3.4 – Misleading graphs
Perceptual distortions – area vs length confusion
In 1980, US dollar value = $1
(area of dollar bill is 100%)
$1
…in 1990, value declined by $.37 to $.63
But the person who drew the graphic reduced each
side of the bill by 37% which reduced the size too much.
Size is exaggerated small suggesting $.40 (area of dollar bill is 40%)
$1
It should have looked like this for $.63
63% area
$1
….in 2010, value declined to $.39.
But the person who drew the graphic reduced each
side size too much.
Size is exaggerated small suggesting $.15 (area of dollar bill is 15%)
$1
It should have looked like this for $.39
39% area
$1
Chapter 7 Page 3 of 7
Watch the scales - abbreviated vertical scale graph is misleading
60
60
percent of
women in
college
50
30
percent of
women in
college
40
30
0
1910 1930 1950 1970 1990 2010
1910 1930 1950 1970 1990 2010
this graphic suggests
“0” in 1950 and less
overall
Watch the scales - non linear scale on graph is misleading
100,000,000,000
computer
calculation
speed
100,000,000
100,000
1
1950 1960 1970 1980 1990 2000
75,000,000,000
50,000,000,000
computer
calculation
speed
25,000,000,000
0
1950 1960 1970 1980 1990 2000
Chapter 7 Page 4 of 7
Percentage change - graph is misleading (new car cost Japan vs USA)
15%
$25,000
12%
$20,000
9%
$15,000
6%
actual
car cost
changes
$10,000
car cost
% changes
3%
$5,000
0
1995
1998
2001
2004
2007
2010
1995
1998
2001
2004
2007
Pictograph - artwork adds visual impact, but can be misleading
WORLD POPULATION IN BILLIONS OF PEOPLE
9
8
7
6
5
4
3
2
1
1804
1927
123 years
1960
1974
1987
1999
Scale is not linear
2012
2024
12 years
2040
2010
Chapter 7 Page 5 of 7
Practice problems page 205
1.)
Abbreviated scale
4”
2”
137’ 0”
10”
8”
6”
4”
2”
136’ 0”
100’
Civic
Jetta
50’
Jetta
Civic
0’
Abbreviated scale suggests large stopping distance difference.
4.)
1cm.
Volume = 1 X 1 X 1 = 1 cm3
2 cm.
Volume = 2 X 2 X 2 = 8 cm3
Sugar production doubled but graphic suggests 8 times increase
by perceptual distortion.
Chapter 7 Page 6 of 7
7.)
5.4 Million
20 Million
The pictograph doesn’t accurately depict the comparison of 20 million vs. 5.4
million because of perceptual distortion…volume confused with length….the
volume of 5.4 million barrels of oil should be much larger.
8.) An accurate bar graph comparison would be:
20 million
15 million
10 million
5 million
0
US
Japan
An accurate sketch comparison would be:
20 million
5.4 million
Chapter 7 Page 7 of 7
11.) Percentage increase is misleading
6
5
4
%
3
change 2
1
0
-1
-2
Consumer Price Index Change
1990
1995
2000
2005
2010
Greatest CPI change
Abbreviated scale is misleading
Consumer Price Index
COST
$700
680
660
640
620
600
580
1990
1995
2000
2005
2010
This is accurate comparison
Consumer Price Index
(Cost of food, fuel, medical, clothing, etc.)
Consumer Price Index
COST
$700
600
500
400
300
200
100
1990
1995
2000
2005
2010
Consumer Price Index
(Cost of food, fuel, medical, clothing, etc.)