# An overview of Kathleen Wickham’s ‘Math Tools for Journalists,’ chapters 1–4

by Dalton Cox

Chapter one: the language of numbers

Journalists committed to precision in reporting need to understand the language of numbers. A good place to begin is by checking the math of one’s sources – look for implausible numbers that may have been altered to give a false impression. Numerical literacy among journalists will signal to audiences the importance of numeracy.

Style Tips

It is best to consult the Associated Press Stylebook when questions arise concerning cardinal numbers.

Generally, spell out numbers below 10 and use figures for numbers above 10, but spell the words cents, million, billion, trillion, ect. When referring to money, use numerals (\$5 million, 1.9 billion tons of gummy bears).

Generally rounding numbers is preferred, but not in all cases. Check the AP Stylebook. Spell out fractions less than one.

For ordinal numbers, spell first through ninth and use numerals for 10th and above.

Never begin a sentence with a number, unless indicating a year.

If an organization uses a number in their name, follow the corporate style in writing your story. Numbers are always used for addresses, dates, highways, percentages, speeds, temperatures, time and weight. AP Style indicates that ages are expressed with figures, but this can vary if a publication uses a different stylebook.

Use the word minus, not a dash or hyphen, to avoid confusion.

Right out numbers in a slang expression (thanks a million).

In a series, retain the appropriate style for each entry.

Chapter two: percentages

Often figures are expressed more clearly if conveyed as percentages. By providing an accurate representation of such a percentage, a reporter is helping an audience better grasp an issue.

Percentage increase/ decrease

Percentage increase/ decrease = (new figure – old figure)/ old figure

Convert the percentage by moving the decimal point two places to the right.

Example: Elon Secondary School reduced its donation to the City Squirrel Sanctuary from \$4,000 to \$600. By what percentage was the donation cut?

600 – 4,000 = -3,400

-3,400/ 4,000 = -0.85

The donation was cut by 85 percent. Poor squirrels.

Percentage of a whole

Percentage of a whole = subgroup/ whole group

Move the decimal point two points to the right.

Low Point University spends \$1.5 million on its badminton team. The entire athletic department budget is \$4 million. What percentage of the budget does the badminton team consume?

1.5 million/ 4 million = .375 = 37.5 percent

Or About 38 percent. That’s a lot of shuttlecocks.

Percentage points

It’s important to distinguish between percentage and percentage point. One percent is one one-hundredth of something. A percentage point may be a different amount.

(new figure – old figure) – old figure = change in percentage POINTS

(change in percentage points)/old figure = PERCENTAGE changed

Simple/annual interest

The amount of money borrowed is called principal. The amount of money paid for the use of principal is called interest.

Interest = principal * rate (as a decimal) * time (in years)

Compounding interest

Compounding means interest is added to the original principal and subsequent compoundings apply the interest to the principal plus the interest of the previous compoundings.

A = monthly payment

P = original loan amount

R = interest rate, expressed as a decimal and divided by 12

N = total number of months

A = [P x (1 + R)^N* x R]/[(1 + R)^N – 1]

*^N refers to ‘N’ to the power of, which means that the result inside the bracket is multiplied N number of times.

Practice Problem

The salary of University President Leopold Lampoon was raised from \$35,000 to \$110,300. What percentage increase was the president’s raise?

Chapter three: statistics

After percentages, the most common numbers that a reporter will likely encounter are statistics. Sources can easily manipulate statistics, so an accurate understanding of the material is essential to informing readers of the truth.

The mean is the sum of all figures in that group, divided by the total number of figures. The median refers to the midway point in a grouping of numbers. The mode is the number appearing most frequent among a set of numbers.

A percentile is a number representing the percentage of scores that falls at or below a designated score. This is often calculated in the occurrence of test taking, such as in reporting on SAT results.

Percentile rank = (number of people at or below an individual score)/ (number of test takers)

This can easily be reversed to tell the number of people who scored at or below a certain point, if you want to know the percentile rank:

Number of people scored at or below that level = (percentile) * (number of test takers)

Standard Deviation

Standard deviation indicates how much a group of figures varies from the norm. A small deviation indicates that figures are grouped around the mean, while a high deviation shows inconsistent results.

To find standard deviation:

Subtract the mean from each score in the distribution.

Square the resulting number for each score in the set.

Calculate the mean for each of these numbers. The result of this is referred to as the variance.

Find the square root of the variance.

Probability

Probability boils down to a ratio.

For Example: The Cox Institute for Made-Up Statistics reports that nearly 2,500 Americans die from quicksand incidents each day. There are about 290 million people in the united States, so the odds of dying in a quicksand incident would be:

2,500 deaths / 290 million people = .0000086

To describe such a probability, divide one by this number:

1 / .0000086 = 116,000

So the odds of dying in a quicksand incident (based on this made-up data) is “one out of 116,000”

Some probability issues are cleaner. Winning the lottery for example is pure chance. Formula used for lottery probability:

Odds of a series of events = Odds of first event * odds of second event * odds of third event, etc.

O = odds

N = number of events

O^N = odds of a series when each is the same

Practice Problem:

In her class, Janet Andrews scored in the 40th percentile on the ACT test.

There are 50 students in her class.

Only the top 30 students will receive the school’s illustrious smarty-pants plaque.

Will Janet receive this distinguished award?

Chapter four: federal statistics

The government provides a constant stream of information of interest to the public. It is important that journalists understand the origin of these numbers and how these numbers are used.

Unemployment

Every month, the U.S. Department of Labor issues a report on unemployment in the United States. The unemployment rate is defined by the percentage of the labor force that is unemployed and actively seeking work.

Unemployment rate = (unemployed/ labor force) x 100

Inflation and Consumer Price Index

U.S. inflation is measured by the Consumer Price Index, which shows the amount of inflation in any given month for eight major product groups: food and beverage, housing, appeal, transportation and recreation. This calculation is determined by a series of surveys on the spending habits of a sample of about 30,000 U.S. families and individuals.

Monthly Inflation Rate = (Current CPI – Prior Month CPI)/ Prior Month CPI * 100

Annual inflation rate

A = Annual Inflation Rate

B = Current month CPI

C = CPI from same month in previous year

A = (B – C) / C * 100

Inflation calculator

A = Target year value, in dollars

B = Starting year value, in dollars

AC = Target year CPI

BC = Starting year CPI

A = (B / BC) * AC

Monthly compounding inflation rate formula

C = cost after one year

K = original cost

I = inflation rate

C = K (1 + [I / 12] ) ^12

Gross Domestic Product (GDP)

GDP is the value of goods and services produced by a nation’s economy.

C = consumer spending on goods and services

I = investment spending

G = government spending

NX = net exports (exports minus imports)

GDP = C + I + G + NX

Trade balance

The trade balance is the difference between the goods and services that a country exports to foreign countries, and its imports from abroad:

Trade balance = Exports – imports

Practice Problem:

In 1999, the Republic of Narnia exported \$55.4 billion worth of fine wine and imported \$16.8 billion worth. What was the trade balance in fine wine?

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