Intro to Descriptive Statistics

STAT 110
INTRODUCTION TO
DESCRIPTIVE STATISTICS
Fall, 2006

Lecture Notes

Joshua M. Tebbs
Department of Statistics
The University of South Carolina

TABLE OF CONTENTS

STAT 110, J. TEBBS

Contents
1 Where Do Data Come From?

1

1.1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1

1.2

Individuals, variables, and data . . . . . . . . . . . . . . . . . . . . . . .

2

1.3

Observational studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4

1.4

Populations and samples . . . . . . . . . . . . . . . . . . . . . . . . . . .

4

1.5

Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5

2 Samples, Good and Bad

8

2.1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8

2.2

Poor sampling designs . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8

2.3

Simple random samples . . . . . . . . . . . . . . . . . . . . . . . . . . . .

10

2.4

Trusting samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

14

3 What Do Samples Tell Us?

15

3.1

Parameters and statistics . . . . . . . . . . . . . . . . . . . . . . . . . . .

15

3.2

Bias and variability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

18

3.3

Margin of error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

19

3.4

Confidence statements . . . . . . . . . . . . . . . . . . . . . . . . . . . .

20

4 Sample Surveys in the Real World

22

4.1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

22

4.2

How sample surveys go wrong . . . . . . . . . . . . . . . . . . . . . . . .

23

4.3

Stratified random samples . . . . . . . . . . . . . . . . . . . . . . . . . .

25

4.4

Questions to ask before you believe a poll . . . . . . . . . . . . . . . . . .

27

5 Experiments, Good and Bad