Table
Favorite TV Shows among Clague Middle School 8th Graders (Nu
(the result of a nonscientific survey -- note the oversampling of girls vs. boys)
Buffy the
Vampire
gender Real World Simpson's 7th heaven Slayer
Male 4 7 1 1
Female 3 4 4 8
TOTAL 7 11 5 9
Favorite TV Shows among Clague 8th Graders (Percentage of Students)
Buffy the
Vampire
gender Real World Simpson's 7th heaven Slayer
Male 27% 47% 7% 7%
Female 7% 9% 9% 18%
Page 1
Table
chool 8th Graders (Number of Students), 1999
of girls vs. boys)
Party of Dawson's
Five Creek Charmed 90210 Total
1 1 0 0 15
5 16 1 3 44
6 17 1 3 59
ge of Students)
Party of Dawson's
Five Creek Charmed 90210 Total
7% 7% 0% 0% 100%
11% 36% 2% 7% 100%
Page 2
chi-square
First question: are the differences between boys and girls signif
What test do we use?
Chi-Square
First we know to calculate the expected values.
To do this, assume that boys and girls would have equal preferences.
OBSERVED VALUES
Buffy the
Vampire
gender Real World Simpson's 7th heaven Slayer
Male 4 7 1 1
Female 3 4 4 8
TOTAL 7 11 5 9
EXPECTED VALUES
Buffy the
Vampire
gender Real World Simpson's 7th heaven Slayer
Male 1.8 2.8 1.3 2.3
Female 5.2 8.2 3.7 6.7
TOTAL 7.0 11.0 5.0 9.0
use Excel's "Function" options and select the chi square test (CHIDIST)
CHI-SQUARE =
0.010825 (which is about 1.1%)
YES, IT IS SIGNIFICANT. THAT IS, THERE ABOUT A 1 PERCENT CHANCE THAT ON
AND 44 GIRLS AND GET THESE DIFFERENCES WHEN THERE IS IN FACT NO DIFFE
Page 3
chi-square
n boys and girls significant?
preferences.
Party of Dawson's
Five Creek Charmed 90210 Total
1 1 0 0 15
5 16 1 3 44
6 17 1 3 59
Party of Dawson's
Five Creek Charmed 90210 Total
1.5 4.3 0.3 0.8 15
4.5 12.7 0.7 2.2 44
6.0 17.0 1.0 3.0 59
(CHIDIST)
ERCENT CHANCE THAT ONE COULD RANDOMLY SAMPLE 15 BOYS
HERE IS IN FACT NO DIFFERENCE IN THE POPULATION AS A WHOLE
Page 4
pie chart
preferred TV shows among boys at Clague Middle School, 1998
Dawson's Creek Charmed
7% 0%
Party of Five
7%
Real World
27%
Buffy the Vampire Slayer
7%
7th heaven
6%
ADVANTAGE: a simple way
to show the big and small
categories
DISADVANTAGES: harder to
include multiple variables
(without multiple pie charts);
takes up a lot of space/ink
(low information/ink ratio).
Simpson's
46%
Page 5
Bubble Chart
Preferred TV shows among Clague students (comparing boys and girls), in percent, 1998
7% 7%
2% This is a "DOUGHNUT CHART"
--
9% a relatively new option on
7% 0% Excel.
7% Fun, but the eye sees
variations in the graphic
27%
design, not in the data.
7%
Real World VERDICT: not very useful
9%
Simpson's here.
7th heaven
7% Buffy the Vampire Slayer
Party of Five
36% Dawson's Creek
Charmed
90210
Boys
18%
47%
11% Girls
Page 6
bar chart 3-D
Preferred TV shows among Clague students (comparing boys and girls), 1998
Female
90210 Male
Charmed
Dawson's Creek
Party of Five
Buffy the Vampire Slayer
Note: 3-D graphics can be appealing
but distracting.
7th heaven
The basic goal: have the eye see
patterns in the data, not just patterns in
Excel graphing capabilities.
Simpson's
Also: harder to see zero values.
Real World Horizontal can sometimes be helpful,
0 2 4 6 8 10 12 14 16
number of students
Page 7
column chart (absolute values)
Preferred TV shows among Clague students (comparing boys and girls), 1998
18
Note: 2-D is easier on the eye.
16
And compared to the pie chart, easier
to include multiple dimensions (gender
14 and show).
But: since many more girls answered
the survey than boys, it is hard to Male
12
easily compare what shows appeal to Female
number of students
boys vs. girls.
10
8
6
4
2
0
Real World Simpson's 7th heaven Buffy the Party of Five Dawson's Charmed 90210
Vampire Slayer Creek
Page 8
column chart (%)
Preferred TV shows among Clague students (comparing boys and girls), in percent, 1998
50%
Note: by converting to percent
45% of total (for boys or for girls),
one can more easily compare
what shows appeal to boys vs.
40% girls.
35%
Male
Female
30%
25%
20%
15%
10%
5%
0%
Real World Simpson's 7th heaven Buffy the Party of Five Dawson's Charmed 90210
Vampire Slayer Creek
Page 9
column chart (%) (2)
Preferred TV shows among Clague students (comparing boys and girls), in percent, 1998
50%
Note: add some gridlines, and have all these lines a
light greyscale so that the data stands out.
45%
40%
The harder question:
35% can you develop a
Male theory to explain these
Female differences in viewing
30% preferences between
teenage boys and girls?
25%
20%
15%
10%
5%
0%
Real World Simpson's 7th heaven Buffy the Party of Five Dawson's Charmed 90210
Vampire Slayer Creek
Page 10