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