Math for Journalists

“Two and two the mathematician continues to make four, in spite of the whine of the amateur for three, or the cry of the critic for five.” -- James Whistler, 1878 “A single death is a tragedy. A million deaths is a statistic.” -- Joseph Stalin “There are three kinds of lies: lies, damn lies and statistics.” -- Benjamin Disraeli

Math for Journalists Is math your friend? Many people enter journalism because they hear that there isn’t too much math. Consider however stories on job growth, population change, cost of living, unemployment, the stock market, trends, and budgets; they all require numbers.

Math for Journalists It doesn’t stop there. The fire had 10 victims, five men and four women. What was the other one? The game started at 9 p.m., one hour after the scheduled 7 p.m. kickoff. How? The $66 million budget is 33 percent higher than the 2003 budget of $33 million. Really?

Handling Numbers First, always check every number in a story. Just as a good reporter would call a phone number to make sure it is correct, that same reporter would check any number in a story.

Handling Numbers Problems often start with percentages. Avoiding those problems start with an understanding of what percentages are. The word “percentage” comes from the Latin Per Centrum, which means per hundred. So 50 percent really means 50 per hundred or 50/100, which is 50 divided by 100, or 0.50.

Handling Numbers Remember that any time you run across a percentage, just move the decimal two places to the left. –50 percent = 0.50 –75 percent = 0.75 –100 percent = 1.00 –150 percent = 1.50

Handling Numbers There’s a secret to understanding percentages and it’s one word: Of. In math lingo, “of” means “multiply.” A bonus word is “is,” which means “equals” in equations.

Handling Numbers Here’s an example. If you invest $10 with a securities company and your year-end statement shows your account is 50 percent “of” your original investment, what “is” your current wealth. If you triple your money, did you increase your wealth 300 percent?

Handling Numbers NOPE! If you triple your $10 investment, you’ve increased your wealth 200 percent. You now have $30, but the increase is $20. That’s 200 percent. This leads to the weird concept of percentage increase.

Percentage Increase A percentage increase means “how much more” you have of something. If your boss shakes your hand and tells you that you will now be making 150 percent of your old $10 hourly salary, you get $15 an hour. Instead, ask your boss for a 150 percent raise. That means you would make $25 an hour.

Percentage Increase Here’s the formula for percentage increase: (New number - Old number) x 100 Old number = Percentage Increase

Percentage Increase So if your $10 salary increased to $25, this is the size of your raise: ($25-$10) x 100 = $15 x 100 = $1,500 $10$10$10 = 150 percent That’s all you need to know about calculating percentage increases, except for one little item.

Percentage Increase Don’t use rounded numbers with percentage increases. Here’s an example. Say the city’s budget is $4.7 million, up from $3.7 million the past year. Using the formula we would arrive at a percent increase.

Percentage Increase Sadly, I fudged the budget numbers. The problem is that I used rounded numbers. The old budget was really $3,651,001. The new one is $4,748,988. ($,748,988 - $3,651,001) x 100 = $3,651,001 $1,097,987 x 100 = $109,798,700 = $3,651,001$3,651,001 percentage increase = percent

Percentage Increase As you can see, percent is different from percent. That’s why you don’t use rounded numbers when you figure the percentage increase. Remember: Whenever you see a chart or graphic that uses rounded numbers, be sure that the footnote makes this clear.

Rounding Numbers To round any number, just select how many digits you want it to have. If the NEXT digit is 5 or more, round UP. If it is less than 5, make no change. For instance, round to the nearest hundredth. You get Round and you get Round either of those to the nearest tenth and you get 51.0.

Percentage Increase There is one more common trap. Let’s pretend that 55 percent of Americans voted in the 2000 election. Now let’s say that 60 percent vote in the 2004 election. So that’s 5 percent increase, right? Wrong. You cannot directly compare the two because the underlying numbers are different: some voters died, some moved overseas, etc.

Percentage Increase What you can say, however, is that the number increased by 5 percentage points. You cannot calculate the percentage increase in this example, unless you have access to the original numbers. Be careful.

More Math Stuff Average. To get the average, just add the numbers in a series and divide by the total numbers you added. For instance, the average of five numbers -- 4, 6, 8, 9 and is 40/5=8. The average is also sometimes referred to as the mean.

More Math Stuff Sometimes averages or the mean can be misleading. Say a company president makes $200,000 and the four employees each make $20,000. This leads to an average salary of $56,000 ($280,000/5=$56,000). While the average is lucrative, the median tells another story.

More Math Stuff Median. The median is the middle number. In the case of the office it’s $20,000. (The series contains $200,000, $20,000, $20,000, $20,000 and $20,000.) Remember: If you see the word median in a story, be sure that the story explains what this number is. A median house price indicates that half the homes cost more and half cost less.

More Math Stuff Rates. Sometimes numbers are so large that the best way to communicate them to the reader is to show their relationship to another, smaller number. There are all kinds of rates. Property tax rates. These are usually expressed as taxes per $100 of assessed property value.

More Math Stuff So, if your tax rate is $1.25 on a house valued at $100,000 with no exemption, the tax bill would be: Tax rate x assessed property value = ($1.25/$100) x $100,000 = $ x $100,000 = $1,250

More Math Stuff Murder Rates. If Sin City had 5,000 murders in a year and Angel Heights had 500 murders that same year, it is possible to compare the two rates. To do it, you have to have the population for each. Fortunately, places like the Oklahoma Department of Commerce and U.S. Census Bureau track the population.

More Math Stuff If Sin City has 8.3 million people and Angel Heights has 400,000 here’s the math: Sin City = 5,000/8.3 million = Angel Heights = 500/400,000 = As you see, it’s tough to compare these two decimals. That’s why murder rates are normally per 100,000 people. To get that number, simply multiply by 100,000.

More Math Stuff Sin City = x 100,000 = deaths Angel Heights = x 100,000 = 125 deaths Now, as we can easily see, Sin City is much safer than Angel Heights, recording deaths per 100,000 population compared with 125 deaths per 100,000 in Angel Heights. These same formulas work with other calculations, such as infant mortality, which is usually expressed in deaths per 1,000 births.

Scientific Polls Editors, and therefore reporters, have a long- standing fascination with polls. Here are some basic rules for handling polls. 1. There must be a scientific basis for the selection of those interviewed. 2. The methodology must be listed in detail. 3. A margin of error must be listed. 4. The above basics must be in the story and in any accompanying graphic.

Numbers in Print As you have noticed, the AP Stylebook has a number of rules for numbers. Keep these in mind. Never spell out ages. He is 5. Never spell out votes. The council voted 5-4. Never spell out percentages. About 14 percent of the class is paying attention. Never spell out money. I found 5 cents. Never spell out numbers with millions or billions. Never spell out height or depth. She is 6-foot-2. The closet is 4 feet by 12 feet. A 3-by-5-foot rug will fit.

Almost Done Since you are now brain-dead, here’s a few more things to pile on while you’re helpless. Very Kiloton: a thousand tons, 1,000 Very Megaton: a million tons, 1,000,000 Very Gigaton: a billion tons, 1,000,000,000 Big Teratons: a trillion tons, 1,000,000,000,000 Itty Millisecond: thousandth, Itty Microsecond: millionth, Itty Nanosecond: billionth, Bitty Picosecond: trillionth,

The Final Stop A few metric conversions as a send off: 1 pint = liters 1 quart = liters 1 gallon = liters 1 inch = 2.54 centimeters 1 foot = meters 1 yard = meters 1 mile = kilometers 1 meter = 100 centimeters 1 kilometer = 1,000 meters