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The Abridged Math Tools for Journalists: Wickham Briefing chpts. 1-4

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Math is something that most journalists tend to shy away from or avoid like the black plague. However, numbers are an important part of journalism and journalists must know how to figure out things like percents and statistics. There is a certain form to writing numbers in articles that must be learned. First of all, journalists should never use Roman numerals in place of Arabic numerals. When it comes to Arabic numbers, single digits (one through nine) should be spelled out but multiple digit numbers are kept in number form. When it comes to larger numbers, you should always round them off unless a specific number is needed. Never start a sentence with a numeral (spell it out), unless it is a date. Or just reword the sentence instead so a number doesn’t start it. Never include more than two or three numbers per paragraph. Be careful of which words to use for certain situations. For example, use over for spatial relationships and more than for amounts and figures.

Percentages

Knowing how to figure out percentages is an incredibly important skill. To figure out percent increase or decrease, use the formula: (new figure – old figure) divided by old figure. Then with that number, you move the decimal two places to the right to turn it into a percent.

Example 1:

Elon University’s number of international students grew from 37 in 1997 to 120 in 2009. What is the percent increase?

120 – 37 = 83

83 / 37 = 2.24 = 224%

The number of students went up 224% percent.

Percentage of a whole is used to determine what part a specific group takes up of a whole group. Use the formula: subgroup / whole group. Move the decimal two places to the right. Percentage points can be figured out by subtracting the old figure from the new figure. Interest can be figured out by using: principal x rate x time (in years). Figuring out payments on loans gets a little more complicated. There are three things needed to calculate monthly payments: original loan amount (represented by P), interest rate (R) and term of the loan (N). The formula is: Monthly payment = [P x (1 =R)^N x R] / [(1 + R)^N -1]

Statistics

Often times journalists will need to interpret studies and surveys, and being able to understand statistics is an important part of this. Finding the mean, median and mode are some of the most simple things to figure out. Mean is the average of all the figures, meaning you just add them up and divide by the total number of figures. The median is the number in the middle of a list of figures, lowest to highest. If there are an equal number of figures, take the two middles ones, add them, and divide by 2. Mode is the most frequent number that occurs in the set. Percentiles are also easy to figure out. A percentile score is based on a relationship with all other scores. To figure it out, take the number of people at or below a certain score and divide it by the number of test takers.

Example 2:

A student gets his media law midterm back and finds out that he received a score of 89. There are 35 students in the class who took the test, and his scores were higher than 20 of them. What is his percentile rank?

20 / 35 = 57th percentile

Standard deviation is something you will often come across in scientific reports, investment documents and other statistical reports. Standard deviation is how much a group of figures differs from the norm. Most journalists won’t have to compute standard deviation but there is a four step formula for doing so: 1. Subtract the mean from each score in the distribution. 2. Square the resulting number for each score. 3. Compute the mean for these numbers. This figure is called the variance. 4. Find the square root of the variance.

Probability is a common thing to figure, especially when it comes to lotto numbers, fatal illnesses and accidents. To show odds, you can divide total deaths by population or show deaths per 100,000 people. Formula = (Total deaths / total population) x 100,000.

Federal Statistics

Federal statistics are numbers from the government on things like unemployment, inflation, GDP, etc. Unemployment rate is the number of those in the labor force unemployed and currently looking for jobs. The labor force is anyone over the age of 16 who has had a job or has recently looked for one. To find unemployment rate, you take the number of unemployed people divided by the labor force, and then multiply that number by 100.

Example 3:

In a small town of 10,000 people, 300 are unemployed of a labor force of 7,000 people. What is the unemployment rate?

300 / 7000 = .0428

.0428 x 100 = 4.28% unemployment

Inflation is based on Consumer Price Index, which shows the amount of inflation per month for eight major product groups including food/beverages, housing, apparel, transportation and recreation. So to find inflation, use: (current CPI – prior month CPI) / prior month CPI x 100.

Example 4:

The CPI of October 2004 was 190.5. November CPI was 191.2. What is the inflation rate for November?

(191.2 – 190.5) / 190.5 x 100 = .367%

Gross Domestic Product is the value of goods and services produced by the nation’s economy. It can gauge the country’s economic situation. For example, when GDP is increasing, the economy is good. If it is decreasing, it often means the country is in a recession. Four things are added to calculate GDP: consumer spending on goods and services, investment spending, government spending, and next exports. Trade balance is simple and is calculated by exported goods minus imported goods.

[All credit goes to Kathleen Woodruff Wickham]

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Written by juliasayers

April 21, 2011 at 10:44 pm

One Response

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  1. Numbers are the high-value details underlying most good reporting, and it is essential that journalists – no matter what field they intend to enter as professionals – should continually keep their math skills honed!

    I was just talking to an Elon math faculty member Friday whose husband is a journalist with the Triad Business Journal, and she said he uses standard deviation and probability a lot in his work.

    Janna

    April 25, 2011 at 2:39 pm


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