Math Tools for Journalists

Abridged Version Chapters 1-4

Newspapers are wrought with numbers: statistics, fiscal amounts, sports scores and more.  When writing an article with numbers, a reporter must use his common sense.  He must ask himself, Does this statistic make sense?  Does this amount of money seem too large, or too small?  Use the same scrutiny when analyzing numerical data that one would with any other information.   As always, reporters should consult their Associated Press Style Guide if they are unsure of how to represent Arabic or Roman numerals, and fractions and percentages in their writing.

When a reporter has to use math in his article that is unfamiliar to the average reader, it is helpful if he compares the numbers to something more tangible or understandable.
Even if a reporter is not using numerals in his article, he still must be careful with the way he represents amounts with his words.  He must be sure that he correctly uses terms such as “less/fewer than,” “more/most,” “farther/further,” and so on.
When working with percentages, the reporter must know a number of formulas.

To determine percent increase or decrease:
Percent increase/decrease = (new figure – old figure) / old figure
*In order to determine the percentage from your result, you must move the decimal point two places to the right.

For instance:
1.    In Atlanta in 2005, 608 people were diagnosed with HIV.  The governor instituted an AIDS awareness program, and in 2008 422 people were diagnosed with HIV.
608 – 422 = 186 ;  186 / 608 = .3059 or 30.6% decrease in the instance of HIV diagnoses in Atlanta between 2005 and 2008.

To determine a percentage of a whole:
Percentage of a whole = subgroup / whole group
For instance:
2.    There are 30 members on the yearbook staff.  Twenty of the members are female.

20 / 30 = .667 or 66.7% of the yearbook staff members are female.

To determine simple interest:
Interest = principal x rate (as a decimal) x time (in years)
For instance:
3.    Lindsay put $100 in a savings account with 3.5 % interest for two years.

100 x .035 x 2 = 7 or $7 in interest over two years.

To determine compounding interest:
A = monthly payment
P = original loan amount
R = interest rate as a decimal and divided by 12
N = total number of months

A = [P x (1 + R)to the power of N x R] / [(1 + R)to the power of N – 1]

When working with statistics, reporters must remember that they can be easily manipulated.  Be sure that readers understand who produced each statistic you report.

Mean- commonly referred to as the “average,” it is the sum of all figures in a group divided by the number of figures in the group.

Median- the midpoint in a group of numbers arranged from lowest to highest.

Mode- the number which occurs most frequently in one group of figures.

Percentile- represents the percentages which fall above or below the target percentage.

Standard deviation- represents how much a group of figures deviate from the norm.

Probability- a ratio which determines the likelihood that something will or will not occur.

Unemployment statistics, which are delivered monthly by the U.S. Department of Labor, Bureau of Labor Statistics, represent the portion of Americans who are unemployed and actively seeking work.

To determine the Unemployment Rate:

Unemployment rate = (unemployed / labor force) x 100

The Bureau of Labor Statistics measures U.S. inflation with a tool called the Consumer Price Index every month in order to track price increases in industries such as food and beverage, recreation, transportation, apparel and housing.

To determine the monthly U.S. inflation rate:

Monthly inflation rate = (Current CPI – Prior Month CPI) / Prior Month CPI x 100

To determine the annual U.S. inflation rate:

A= Annual Inflation Rate
B= Current Month CPI
C= CPI from the same month in previous year

A = (B – C) / C x 100

The Gross Domestic Product measures quarterly the value of all the goods and services produced in the U.S. economy.

To determine GDP:

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 compares the number of goods and services the United States imports versus the number they export.

To determine trade balance:

Trade Balance = Exports – Imports