Numbers in the Newsroom

147 Pages·2001·1.235 MB·English

by  Sarah Cohen

This e-book version of Numbers in the Newsroom was
produced in collaboration with the Donald W. Reynolds
Journalism Institute (RJI) at the Missouri School of
Journalism. For more information about the RJI Newsbook
Project visit: www.rjionline.org/newsbooks.
iii
Numbers in
the Newsroom
UsiNg math aNd statistics iN News
SECOND EDITION
By Sarah Cohen
Investigative Reporters & Editors, Inc.
Editor:
Dan Claxton
Design:
Wendy Gray
ISBN 0-9766037-1-3
One in an ongoing series of beat books and reporting guides
by Investigative Reporters & Editors, Inc.
Please direct comments and suggested updates to:
[email protected].
Copyright © 2014 by Investigative Reporters & Editors, Inc. and Sarah Cohen
iv IRE Beat Book: Numbers in the Newsroom
v
Foreward
Foreword
This guide would not have been possible without advice and
help from many corners. The original version was informed by
practioners Neill Borowski then of The Philadelphia Inquirer, Dan
Browning of the Minneapolis Star-Tribune, Ron Campbell of the
Orange County Register, Chris Callahan now dean of Arizona
State University’s journalism school, Jo Craven McGinty of The
Wall Street Journal, Stephen Doig of Arizona State University,
Ford Fessenden of The New York Times, Dan Keating of The
Washington Post, Jennifer LaFleur of the Center for Investigative
Reporting, Andy Lehren of The New York Times, Philip Meyer of
the University of North Carolina and Patrick Remington of the
University of Wisconsin. Over the years, we’ve received input
from many more corners.
Thanks to all of those who helped focus this handbook and
provide suggestions. Thanks also to Wendy Gray for graphics
assistance and design, Lauren Grandestaff for editing and Zana Lo
of IRE for seeking additional resources for reporters.
If you just want an overview of the concepts in this book, feel
free to watch the video created for Columbia Journalism School’s
Stabile program for a Spring 2014 class at https://www.youtube.
com/watch?v=lZjsCycecNc
And special thanks to Len Bruzzese, and Brant Houston at IRE
for shepherding this original project, and Dan Claxton and Mark
Horvit for this newer effort.
vi IRE Beat Book: Numbers in the Newsroom
table oF coNteNts
INTRODUCTION
CHAPTER 1: WHAT’S A NUMBER? ...................................1
Seven big tips to keep your copy number-free and fair .....................2
Good habits for reporting with numbers ................................9
CHAPTER 2: A NEWSROOM MATH GUIDE ............................11
The pers: Fractions, rates, percents and per capita ........................11
Fractions and percents ........................................12
Per person (or per capita): Death rates, crime rates and other rates .......16
Rates for large numbers – Per person averages ................16
Rates for small numbers – Crime, death and other rare events .....17
Going further with the pers: Doing math with rates .......................21
Adding and subtracting rates ...................................21
Rates of rates, or “relative risk”. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
A note on significance testing and rates ...........................21
Measuring change ................................................26
Simple differences (or actual change) .............................26
Percent change, or percent difference ............................28
Reversing percent differences .............................28
Percentage point difference vs. percent difference –
One word, big difference ................................31
Going further with changes: Annual rates and inflation adjustment ............34
Annual rates .....................................................34
Projecting changes into the future ..........................36
Converting total change to annual rates. .....................38
Adjusting for inflation ........................................40
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Understanding averages – Means, medians and modes ....................44
The simple average, or mean ...................................44
Medians or middle values .....................................45
Modes or common values .....................................47
The Anti-Lake Wobegon effect: Is anyone average? ..................47
Going further with central tendency: Averaging averages,
changes and significance ...........................................50
The problem of averaging averages ..............................50
Weighted averages .....................................50
Grouped medians ......................................52
Working with averages and rates ...........................52
Some figures to troubleshoot your averages ........................55
Standard Deviation .....................................55
Trimmed mean ...................................................56
The problem of comparing averages over time ...........................58
CHAPTER 3: WORKING WITH GRAPHICS .............................61
Types of charts ...................................................62
Bar vs. fever charts ...........................................62
The problem of scale ..............................................66
CHAPTER 4: THE STANDARD STORIES ...............................73
The budget story: Using percentages, inflation adjustment
and measures of change ............................................73
Understanding the budget .....................................73
Tips for preparing for the budget season. . . . . . . . . . . . . . . . . . . . . . . . . . . 75
Property taxes and the dreaded “mill” – Using rates .......................75
Figuring property taxes .......................................76
Three examples of property taxes ................................78
viii IRE Beat Book: Numbers in the Newsroom
The weather story: Earthquakes, hurricanes and wind-chill – Using indexes .....81
Earthquakes and the richter scale ................................81
Hurricanes and Tornadoes .....................................82
Heat indexes and wind-chill factors ..............................83
Stadiums, layoffs and other economic predictions – Using historical averages ...84
How to deconstruct an economic impact statement ..................85
Who’s No. 1? School reports, health care rankings and places rated –
opinions in numbers ...............................................88
Reporting on indexes and rankings ..............................90
CHAPTER 5: SURVEYS AND POLLS –
NUMBERS AS SUMMARIES AND GUESSES ............................95
Know your pollster ................................................95
Question wording and sequence ................................97
Sampling method and response rates .............................98
The margin of error (sampling error). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
The elements of sampling error .................................100
Calculating your own margin of error .......................101
More poll and survey tips .....................................106
CHAPTER 6: THE 10 MOST WANTED LIST: MISTAKES IN THE NEWS
FROM SIMPLE MATH TO LAPSES IN JUDGMENT .......................107
10. Flipped probabilities and the cancer cluster .....................107
9. The magic rubber band, or misunderstanding “The law of averages” ...108
8. Overcooking vegetables with an average of an average .............109
7. Who cares? or Losing sight of your base .........................110
6. False precision, or the Mr. Spock disease ........................110
5. The If... then disease: Confusing Cause and effect .................111
4. Ignoring the little voice inside you .............................113
3. Inadequate sourcing ........................................113
2. Packing numbers into a story: Compression, not selection, of facts ....114
1. Letting 10-2 paralyze us .....................................114
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CHAPTER 7: LOTTERIES, LIGHTNING STRIKES AND LONGEVITY –
A NOTE ON PROBABILITIES ..........................................115
Calculating a probability ..............................................116
Lotteries ..........................................................118
Small probabilities x big numbers = big mistakes ...........................120
Coincidences over time – combining probabilities ..........................122
Stock pickers .......................................................123
Batting streaks ......................................................124
Cancer clusters ......................................................125
CHAPTER 8: RESOURCES .............................................127
At IRE .............................................................127
Websites ..........................................................129
Fractions and percentages chart .........................................132
x IRE Beat Book: Numbers in the Newsroom