CHAPTER 3 CHAPTER 3 Graphical PresentationsGraphical Presentations
Types of VariablesTypes of Variables
Qualitative - categories which can be named
- Classification : Fr., So., Jr., Sr.
- Occupation
Quantitative - “meaningful” numerical values
- SAT score
- Height, Weight, Age
Quantitative Variables may Quantitative Variables may be be discretediscrete or or continuouscontinuous
Discrete - possible values for the variable can be listed
- number of brothers
- number of Heads out of 10 tosses of a coin
Continuous - different values can be arbitrarily close
- height
- weight
Blood Group Data – “raw data”Blood Group Data – “raw data”
Patient # Blood Type 1 O 2 A 3 A 4 O 5 B 6 O 7 A 8 AB . . . . . .
Pie Chart - Blood Group Pie Chart - Blood Group DataData
46%
40%
10%4%
O
A
B
AB
Bar Chart - Blood Group DataBar Chart - Blood Group Data
0
10
20
30
40
50
O A B AB
Blood Group
Pe
rce
nt
APTITUDE TEST scores for 20 applicants :
Raw Data: 68, 72, 91, 47, 52, 75, 63
55, 65, 35, 84, 45, 58, 6169, 22, 46, 55, 66, 71
Ordered List:22, 35, 45, 46, 47, 52, 5555, 58, 61, 63, 65, 66, 6869, 71, 72, 75, 84, 91
Ways to Display Quantitative Ways to Display Quantitative DataData
Dot Plot for Aptitude DataDot Plot for Aptitude Data
Score
Stem-and-Leaf DiagramStem-and-Leaf Diagram
HISTOGRAMHISTOGRAM
for quantitative data
“sort of like” bar chart
represents % by area
Density ScaleDensity Scale-sets height of block so that
resulting area is % in that class interval% in that class interval
% in class intervaldensity scale ( % per unit) =
length of class interval
SummarySummary HISTOGRAM -- for quantitative data -- represents % by area (use density
scale) -- total area in blocks is 100%
-- each histogram should have: - title - axes should be “numbered” and labeled
BAR CHART -- for qualitative data -- represents % by height
(what’s wrong with this (what’s wrong with this histogram?)histogram?)
0
0.6
1.2
1.8
2.4
3
40 55 70 80 9520