**Abridged Math Tools for Journalists – Chapter One**

by Lesley Cowie

Although journalists are generally fixated on words, they must analyze and interpret numbers for their stories. Numbers add support and credibility to facts. They also help readers understand the scope and significance of the information in the story.

In addition to interpreting the numbers, journalists should use the numbers in the proper context of their stories. When done properly, this will allow the reader to understand the material even easier. Some of the most important style, writing and language tips are as follows:

Numbers help the reader understand the significance of an issue. Percentages are often used to show change or the parts of a whole. Specifically, journalists use percentages for four reasons: percentage increase, percentage decrease, percentage of the whole, and percentage points.

The formula for the first task is as follows: percentage increase – percentage decrease (new figure – old figure)/old figure. This number may be converted to a percentage by moving the decimal two places to the right.

The formula for percentage decrease is the same as the formula for percentage decrease. The only difference is that the result will be a negative number.

To calculate the percentage of a whole, one must divide the subgroup into the whole group. This will give them the portion of the whole. Once again, to convert the number to a percentage, move the decimal point two places to the right.

It is important to distinguish between *percent* and *percentage point*. One percent is one one-hundredth of something. One percentage point might also be one one-hundredth of something, but one percentage point could also be something other than one percent.

**Calculating interest**

Percentages may also be used for calculating interest. Simple interest is the basic form of this type and is most commonly used. The formula for simple interest is principle x rate (as a decimal) x time (in years).

When calculating simple interest, the amount of money borrowed is called the *principal*. Money paid for the use of money is called *interest*. The *rate* is the percent charged for the use of money. Interest charges depend on the length of time that the money is borrowed; interest is generally calculated on a yearly basis.

Compound interest is a little more complicated because the interest is added to the original principle. Subsequent compoundings apply the interest to the principle plus the interest of the previous compoundings.

**Interpreting statistics**

After percentages, statistics are the next most common form of numbers in journalism. Statistics convey averages, accurate inferences and information regarding crime reports. Because journalists frequently review surveys, it is important that they can interpret and communicate the results effectively.

The mean is the sum of all the numbers in a series divided by the total number of figures. The mean is commonly called the “average.”

The median is the figure in the middle of the series of numbers. In order to find the median, it is best to rewrite the figures from lowest to highest. From there, find the number that has the same number of figures before and after it. This number will be the median. If there are two numbers in the middle of the series who share the same number of figures before and after them, find the mean of these two numbers, and the median will be the result.

The mode is the number that appears most frequently in a series. If each number appears only once, there is no mode. If several numbers appear more than once, they are all the mode.

A percentile is a number that represents the percentage of scores the fall at or below the designated score. A percentile rank may be determined by dividing the number of people at or below an individual score into the number of overall test takers. To determine the number of people at or below an individual score, one might multiple the given percentile by the number of test takers.

The standard deviation of a series indicates how much a group of figures varies from the norm. This kind of statistical data is often viewed graphically in a bell curve. The middle of the curve, which is the highest point, is the mean. The steeper the bell, the smaller the standard deviation.

Stories about the lottery, traffic accidents, and fatal illnesses often contain probability. To show health-related figures, one could calculate as follows: deaths per 100,000 people = (total deaths/total population) x 100,000. When it comes to stories about illnesses, they are usually not completely random events.

**Communicating math for the public good**

The federal government often uses numbers to inform the public about inflation and/or unemployment. Journalists must understand what these figures mean and how they were determined. Inflation is measured by the Consumer Price Index. This number, determined by the Bureau of Labor Statistics, shows the amount of inflation in any given month for eight major product groups, including food and beverages, housing, apparel, transportation and recreation. The monthly inflation rate could be determined as follows: (Current CPI – Prior Month CPI)/Prior Month CPI x 100. To calculate unemployment, one would divide the unemployed into the labor force and then multiply by 100.

Gross Domestic Product is the value of goods and services produced by a nation’s economy. This number helps gauge the direction of the country’s economy. When GDP is increasing, the economy is considered healthy. The change in GDP is what most people watch.

GDP is reported quarterly, and the rate of GDP is reported as an annual rate. The “real” GDP holds the prices of the measured items constant to the prices they were in 1996.

The trade balance is the difference between the goods and services a country exports to foreign countries and those it imports. The seven major categories of exports and imports are capital goods, services, industrial supplies, autos and auto parts, consumer goods, food and beverages and “other.” The trade balance can be calculated by subtracting the amount of imports from the amount of exports.

These are the basic, and most common, ways to interpret and use numbers in journalism. It is clear that these formats support facts in a story and help the reader to understand the overall significance of the issue.

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