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Workina with

Numbers and Statistics

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Charles Livingston PaulVoakes

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Working with Numbers and Statistics

A Handbook for Journalists

LEA'S COMMUNICATION SERIES

Jennings Bryant/Dolf Zillmann. General Editors Selected titles in Journalism (Maxwell McCombs. Advisory Editor) include:

FriedmannI DunwoodI Rogers ? Communicating Uncertainty: Media Coverage of News and Controversial Science Garrison. Professional Feature Writing. Fourth Edition Iorio. Taking It to the Streets: Qualitative Research in Journalism Livingston/Voakes ? Working with Numbers and Statistics Merritt/McCombs ? The Two W's of Journalism: The Why and What of Public Affairs Reporting Roush. Show Me the Money: Writing Business and Economics Stories for Mass Communication Salwen/Garrison/Driscoll ? Online News and the Public Titchener ? Reviewing the Arts. Second Edition

For a complete list of titles in LEA's Communication Series, please contact Lawrence Erlbaum Associates, Publishers, at .

Working with Numbers and Statistics

A Handbookfor Journalists

Charles Livingston Paul Voakes

LAWRENCE ERLBAUM ASSOCIATES, PUBLISHERS

2005 Mahwah, New Jersey

London

Copyright ? 2005 by Lawrence Erlbaum Associates, Inc.

All rights reserved. No part of this book may be reproduced in any form, by photostat, microform retrieval system, or by any other means, without the prior written permission of the publisher.

Lawrence Erlbaum Associates, Inc., Publishers 10 Industrial Avenue Mahwah, New Jersey 07430

Cover design by Melissa Cassutt Page design by Elena A. Fraboschi

Library of Congress Cataloging-in-Publication Data

Livingston, Charles. Working with numbers and statistics: A handbook for journalists /

Charles Livingston, Paul Voakes. p. cm. - (LEA's communication series)

Includes bibliographical references and index. ISBN 0-8058-5248-4 - ISBN 0-8058-5249-2 (alk. paper)

1. Mathematics. 2. Statistics. 3. Journalism-Mathematics. I. Voakes, Paul S. II. Title. III. Series.

QA39.2.L592004 510-dc22

2004054123

Books published by Lawrence Erlbaum Asssociates are printed on acid-free paper, and their bindings are chosen for strength and durability.

Printed in the United States of America 10987654321

Contents

Preface

vii

Chapter 1. Introduction

1

Chapter 2. Some Fundamentals

7

2. 1. Percentages

7

2.2. Adjusting for Inflation

10

2.3. Working with Probability

12

2.4. Interest, Simple and Compound

14

2.5. Rates (Ratios)

15

2.6. Scientific Notation

16

2.7. Names of Numbers

16

2.8. Rounding

17

2.9. Conversion Factors

19

2.10. Issues of Logic

21

2.11. Decoding Budgets

23

2.12. Taxes

25

2.13. Business Basics

28

Chapter 3. Describing Data

31

3.1. Averages

31

3.2. Variation

36

3.3. Correlation

40

3.4. Interpreting Tables

43

3.5. Displaying Data with Graphs

47

Chapter 4. Estimation

51

4.1. Polling Data: Estimating a Proportion

52

4.2. Estimating a Mean

55

4.3. Other Estimates

58

Chapter 5. Inference: Drawing Conclusions from Data 61

5.1. Hypothesis Testing and p-Values

61

5.2. Correlation

64

5.3. Fallacy: Regression to the Mean

69

v

Chapter 6. Surveying and Experimental Design

71

6.1. Surveying Techniques

71

6.2. Experimental Design

73

6.3. Observational Studies

75

Chapter 7. Advanced Statistics

77

7.1. The Normal Distribution

77

7.2. z-Scores

80

7.3. Estimates

81

7.4. Hypothesis Testing

83

Chapter 8. Cautions and Fallacies

89

8.1. Correlation and Causation

89

8.2. Beware the Non-Random Sample

90

8.3. A Large Population does not Demand a Large Sample 92

8.4. Comparing Numbers versus Comparing Percentages 92

8.5. Percentage Change versus Percentage Point Change 93

8.6. Regression to the Mean

93

8.7. Nonexistent Trends

94

8.8. Probability with Conditions

95

8.9. Combining Overlapping Quantities

95

8.10. Probability versus Odds

96

Chapter 9. Excel and the Internet

99

9.1. Web Resources

99

9.2. Working with Excel

99

Chapter 10. Writing with Numbers

105

10.1. Use Numbers - But Sparingly

105

10.2. Alternatives to Raw Numbers

107

Appendix: Table of CPI, 1920-2004

109

Index

111

Preface

Our interest in writing a book about mathematics and statistics for journalists was inspired by our work designing and teaching a course for journalism students. The development of that course was supported by a Mathematics Throughout the Curriculum grant from the National Science Foundation, with Principal Investigator Dan Maki, professor of mathematics at Indiana University. We thank the NSF and Dan for their support.

Andrew Ellett, a mathematics graduate student at Indiana University, assisted us and later taught the math-stat journalism course. We learned a lot from Andrew about how to approach the educational needs of our audience, and he gave us excellent feedback on our efforts. Steve McKinley, a lecturer in the Department of Mathematics, also gave us valuable feedback, as did our colleague, Steen Andersson. We are grateful to Andrew, Steve and Steen for their contributions. Finally, one article, "How numbers can trick you" by Arnold Barnett (Technology Review, October 1994), was especially informative to us.

We have gained much from our students. Their feedback was invaluable as we learned to teach mathematics for journalists. This book is far better for our experiences with them.

The book was produced using the typesetting language LaTex. Elena Fraboschi designed the book and did the typesetting, transforming our bare-bones outline into what we hope the reader finds an attractive and appealing environment to enhance their understanding of mathematics and statistics.

Our deepest appreciation goes to our wives, Lynn Greenfield and Barbara Voakes, for their patience and encouragement during the development and writing of this book.

vii

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