Math for communicators

1. Math for communicators

2. In general • Many press releases/stories/ads are based on numbers. • Familiarity with basic math is necessary to convey the info the numbers represent to your audience. • If you aren’t good at math, ask for help. • Online tools can be helpful.

3. Precision • Numbers are precise • We need to accurately convey that precision in our ads, press releases, news reports • Numbers help us express clearly, concisely the amount of change, trends, etc.

4. Percentages • As proportion of part to whole- Divide the part by the whole- Move the point two spaces right- Add the word “percent” • For example- Jones got 215 of the 312 votes cast- 215 divided by 312 is .6891- Jones got 68.9 percent of the vote

5. Percentages • To express change- Determine the base number and the new number.- Find the difference by subtraction.- Divide the difference by the base. • For example:- Enrollment last year was 12,310; this year it’s 13,200.- The difference is 890.- 890 divided by 12,310 is .0722- Enrollment has grown by 7.22 percent

6. For example • In a city of 42,000 population, 6,260 residents are Hispanic. What is the city’s percentage of Hispanic residents? • Last year, 615 students graduated from the school. This year there were 589 graduates. By what percentage have graduates decreased?

7. Answers • 6,260 Hispanic residents divided by 42,000 total population = 0.1490. Move the decimal two places to the right – 14.9 percent. • Base number is 615. Difference is 26. Divide 26 by 615 and it equals .0422. Decline is 4.2 percent.

8. Measures of central tendency • The mean (average)- Add the individual numbers- Divide the sum by the number of numbers.- The result is the mean. • For example:- Your grades on quizzes are 4.0, 3.7, 3.7, 2.7, 4.0, 3.3- The total of the six grades is 21.4- 21.4 divided by 6 = 3.56

9. For example • Six people are on a bus. • Their incomes are $35,000, $79,000, $65,000, $53,000, $27,000 and $39,000. • What is their mean income? • The six added together equals $298,000. Divide that total by six, and the result is $49,666.

10. Measures of central tendency • The median- Find the middle number- If you’ve got a sample of 21 cases, the median is the number with 10 numbers greater than it and 10 numbers smaller than it.- In even-number sets, average the two in the middle.

11. Median income on bus • $27,000; $35,000; $39,000; $53,000; $65,000; $79,000 • Since the number of cases is even, add the two middle cases and divide by 2. • $39,000 + $53,000 = $92,000. $92,000 divided by 2 equals $46,000.

12. Back to the bus • Bill Gates gets on the bus. • His income is $100 million. • Which measure makes more sense to provide a snapshot of who is on the bus – the mean or the median?

13. Median income with Gates • $27,000; $35,000; $39,000; $53,000; $65,000; $79,000; $100,000,000. • Middle number is $53,000. • If we had used the mean to express the makeup of the bus ridership, we’d say the average person on the bus earned $14,328,285.

14. Measures of central tendency • The mode- Most frequent number in a set- If each number appears once, there is no mode- If several numbers appear the most, they are all modes- Not a very practical usage.

15. Mills in Michigan • Mills are the units used by Michigan governments to levy taxes on property. • A mill is a tax of $1 on each $1,000 of taxable value of land, buildings and business equipment and machinery. • Taxable value can be no more than half of market value.

16. Millage calculations • Choose a representative taxable value, $50,000 for example. • Divide it by 1,000. • Multiply the result by the millage rate. • If a city levies 2.35 mills, the owner of a home with a taxable value of $50,000 would pay $117.50 in taxes.

17. Surveys • The best use of survey technique is to use a sample to represent the whole. • A sample will not be representative unless it is truly random. • In a random sample, every member of the whole group has an equal opportunity of being chosen.

18. Convenience samples • Convenience samples – the first five people you meet outside the library, for example – are not representative. • Their only valid use is to generate good quotes that illustrate points of view determined by other, more valid means. • Don’t misrepresent convenience samples as random samples.

19. Writing withnumbers • Cite sources for all statistics. • Long lists of figures are difficult to read in stories. Charts and graphs may be a better option. • Round off numbers usually after two places. For example: $1.35 million rather than $1,349,276. • Always double-check your math and verify statistics a source gives you. • If you don’t understand the numbers, get an explanation.

20. Check the math • If given statistics, check the math. • For example – you are told the budget is X percent larger than last year. • Do the math and check. • Journalism is the discipline of verification. • PR, advertising need to be based on sound information.

21. Numbers and style • When writing, follow the general rules under “numerals” and other number references in the stylebook. • Spell out fractions: one-tenth, two-thirds. • Ranking – when using numbers to indicate a position, use first, second, third … ninth. Spell out larger than 10 – 10th, 11th, 23rd, etc.

22. Corporate names • Here, we vary from the common AP style rules. • Instead, use the company’s official name:- Fifth Third Bank.- Century 21 Real Estate.

23. Minus, informal references • Use the word minus, not the symbol, to avoid confusion:- It was minus-21 on Thursday.- It was 21 below zero Monday. • In informal or slang references to numbers, spell out:- Thanks a million.- He was a million to one shot to win.

24. Questions?