Math Tools for Journalists: tips from Wickham’s book
By Kate Austin
11/2/08
CHAPTER 1: THE LANGUAGE OF NUMBERS
Chapter one of Wickham’s book discusses the language of numbers. It is highly important to double-check the math of speakers, reports and budgets. One never knows if someone may have tweaked the numbers to sound better.
One must also know when it is appropriate to tweak the numbers in regards to rounding. Knowing when it’s appropriate to round should be straightforward. In Wickham’s example, one would never round with the number of deaths in a fire, but it is inconsequential to round the amount of salt used on town roads, increasing readability.
When beginning a sentence with a number, one must spell the number out, or better yet, alter the sentence so that it does not begin with a number.
Finally, one of the most important things a writer can do when working with numbers is to digest the numbers for the reader. Wickham suggests using analogies, storytelling tactics and graphics to explain numbers to readers.
This digestion of the numbers includes the use of appropriate language when working with numbers. For example, when speaking of figures and amounts use “more than” rather than “over” to explain a greater value.
CHAPTER 2: PERCENTAGES
There are many formulas that are useful for percentages in the news. This falls again on the digestion of numbers by the reporter for the reader. Wickham says one should never leave it to the reader to calculate percentages.
Some useful formulas include: the formula for percentage increase/decrease: (new figure – old figure) / old figure (.001) = percentage increase/decrease; for salary increase: original salary x percent increase = dollar amount of salary increase for first year; the percentage of a whole: subgroup / whole group (.001) = percentage of whole.
Another set of important formulas is used for sports statistics such as batting average, slugging percentage, and earned run average.
It is important, when working with percentages, that one realizes there is a difference between percent and percentage point. One percent is equal to one-hundredth of something, but a percentage point is based on the numbers within the equation and therefore could be anything.
Many of the numbers in a news report will be monetary amounts. Some main formulas for this topic tell how to find payments on loans (monthly payment = [original loan amount x (1 + interest rate)^total number of months x interest rate] / [(1 + interest rate) ^ total number of months -1]).
Sample problem:
Jeff Jefferson took out a loan for three semesters (15 months). How much must Jeff pay each month on a loan of 4,600 at 5.5 percent interest, compounded annually, assuming he pays back the loan in total after 15 months?
CHAPTER 3: STATISTICS
According to Wickham, statistics are important for reporting crime rates, average cost of food and student test scores. Statistics can be used to make inferences about a subject. Mean, mode and median are three ways to assess data and find an average, a middle number and a most frequent number from a set of data. It is important to know how to assess when each of these would be appropriate in most accurately representing data.
Percentiles are used to show a number in relation to the other numbers; for example, a percentile score is in relation to all the other scores. The simple formula for this according to Wickham, is: Number of people at or below an individual score / number of test takers = percentile rank.
Sample problem:
Bob Brown received the results of his state achievement tests. He received an overall score of 78. Bob found from reading the brochure that came with the results that 5,300 students took the test. Bob’s score is equal to or higher than the scores of 2,438 students. What is Bob’s percentile rank?
2,438 / 5,300 = 46th percentile
Probability can be useful to put things in perspective. Especially in regards to death numbers, or traffic accidents, where the numbers seem high but put in perspective the probability of this happening to someone is low. It is also common for health related figures to show the number of occurrences “per 100,000 people.” Wickham’s formula for this is: Deaths per 100,000 people = (total deaths / total population) x 100,000.
Sample problem:
8,045 Americans died in plane crashes over the past month. What is the probability that an American will die in a plane crash (using the “per 100,000 people” method)?
(8,045 deaths / 290 million people) x 100,000 = 2.77
CHAPTER 4: FEDERAL STATISTICS
Federal statistics such as unemployment rates and inflation rates are important to understand. The government finds the unemployment rate by the formula, (unemployed / labor force) x 100.
Another important way to understand numbers is for inflation. “Adjusted for inflation” is a common phrase meaning that the number has been changed to show what it would be equal to today. This can be found by the formula: target year value = (starting year value/ starting year Consumer Price Index) x target year CPI. The CPI values can be found on the BLS website.
Sample problem:
Jenna Jackson started as an editor in July 1990 for a salary of $7,600 a year (CPI July 1990 = 130.4). How much would this be in August 1990 dollars (CPI August =131.6)?
(7,600 / 130.4) x 131.6 = $7,670
