Percentages, statistics, and more: basic math tips from MTJ

1. The Language of Numbers

Numbers are an essential part of journalism, and any good reporter should be able to understand and express information involving numbers. Becoming numerically literate means breaking down numbers and repackaging them in a palatable way for readers. Below are some ways to make important numerical information useful in your reporting.

Simplify, simplify, simplify

  • Spell out shorter numbers, but use numerals for longer numbers
  • Round off big numbers unless specificity is required
  • Do the math for readers
  • Use analogies or graphics to make numbers easy to interpret
  • Be precise with comparative language

2. Percentages

Percentages are one of the more commonly encountered elements of numerical representation in journalism, but also some of the most difficult to work with. Below are some of the most important formulas and definitions to know when working with percentages.

Percentage increase/decrease

Helpful for stories charting funding, budget, or salaries across multiple years

  • (new figure – old figure) / old figure
  • Convert to percentage by moving decimal two places right

Percentage of a whole

Helpful for providing scale by putting amounts in perspective

  • subgroup / whole group
  • Convert to percentage by moving decimal two places right

Percentage points

Percentage is the part of a whole, percentage points compare two or more percentages

Simple/annual interest

Used to describe interest on money borrowed

  • Money borrowed is called principal, money paid for the use of money is called interest
  • Interest = principal x rate (as decimal) x time (in years)

Compounding interest

Describes interest added to the original principal and subsequent compoundinG

  • Formula below for payments on loans
  • A = monthly payment, P= original loan amount, R= original interest rate, expressed as decimal and divided by 12, N= total number of months
  • A = [P X (1 + R)N X R] / [(1 +R)N – 1]

3. Statistics

Just like percentages, statistics are entirely vital to your job as a journalist. In the right contexts, they can be incredibly useful tools in your storytelling. But first, you must have an understanding of what statistics mean and how to properly contextualize them. Below are some examples of helpful statistical concepts.

Mean

Commonly referred to as “average”, helpful in showing general trends

  • Add up all figures and divide by total number of figures

Median

Middle number in a group, not as mathematically valuable as mean

  • Put all figures in an order from lowest to highest, median is the figure in the middle of that order

Mode

The number appearing most frequently in a group

When to use mean, median, or mode

  • Mean is most appropriate when figures are all over the place, and average is the best way to establish a reasonable middle
  • Mode is most appropriate when a few outliers would skew an average, and the most commonly repeated number is the best representation of the usual figure
  • Median is most appropriate when one or more outliers would make a mean inaccurate, and mode doesn’t fully express a common example of the figure

Percentile

Describes the number of scores that fall below the provided score, indicated rank relative to competition

  • Percentile rank = (number of people at or below an individual score) / (number of total people who scored)

Standard Deviation

Common in scientific reports

  • Indicates how much a group of figures varies from the norm
  • Subtract mean from each score, square resulting number for each score, compute the mean for those numbers (that mean is called the variance), find the square root of the variance

Probability

Using probability to express likelihood can help reader’s understand potential future events

  • Instances occurred divided by total population
  • Lottery is pure chance

4. Federal Statistics

The federal government provides a number of statistics to the general public, sharing information covering the general economic welfare of the nation. These figures, when properly interpreted, can bear value for journalists trying to inform themselves and the public about the state of the nation’s economy and how it will affect people. Below are some common federal statistics, what they mean, and how to use them.

Unemployment

A helpful barometer to compare employment of the national workforce across different years and eras

  • Monthly number indicating the amount of the labor force (people over the age of 16 who have a job or have looked for one in the past four weeks, except unemployed people not actively seeking work) that is employed (having done some work for pay in the week before the survey)
  • Unemployment rate = (unemployed / labor force) x 100

Inflation and Consumer Price Index (CPI)

Useful for showing readers the fluctuating value of their money and the cost of the goods they buy

  • U.S. inflation is measured by the CPI, showing the amount of inflation for eight major product groups through a survey of 30,000 individuals
  • Monthly inflation rate = (Current CPI – Prior Month CPI) / Prior Month CPI x 100

Adjusting for Inflation

A way to express historical dollar values with their their modern worth equivalent

  • A = Target year value in dollars, B = Starting year value in dollars, AC = Target year CPI, BC = starting year CPI
  • A = (B/BC) x AC

Gross Domestic Product (GDP)

Increasing GDP indicates a healthy economy, decreasing GDP indicates a worsening economy that may be in a recession. The change in GDP is a more valuable statistic than the level of the GDP itself

  • 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 difference between goods and services exported to a foreign country versus those imported. Limited use, but relevant when talking international trade

  • TB = Exports – imports
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