Public Speaking

10 0 CHAPTER^8 Choosing Supporting Materials

2. Make numbers come alive by comparing them to something already in your listeners’
   experience. We often hear big numbers such as $17.5 trillion, our national debt,
   but what does that really mean? Many online sources try to help you visualize it.
   For example, stack of $1 bills would reach past Uranus.^14 And if your salary were
   $40,000 a year, it would take you 25 million years to earn $1 trillion. If you live
   to be eighty, you would have to save $34 million every day of your life to have $1
   trillion. Multiply that by 17.5.^15

Think Critically about Statistics

Common statistics include the mean, median, mode, percentages, and ratios.

The mean is the average of a group of numbers. To calculate it, add up the individ-

ual items and divide by the total number of units measured. The mean is skewed when

extreme figures at either end of the range make the comparison less useful. Just average

one billionaire’s income and the annual incomes of nine people who work for minimum

wages to understand the limitations of the mean.

The median is the middle number in a set of numbers that have been arranged into

a ranked order: half the numbers are above and half below. For example, home prices in

a particular area are typically stated as a median, which balances the very expensive man-

sions against the less expensive fixer-uppers.

The mode is the number that appears most commonly. For instance, on some

college campuses, a few first-year students may be 16 years old, more are 17, some are in

their twenties, thirties, or forties, but most are 18—the mode.

Percentages show the relationship of a part to the whole, which is represented by

the number 100. You’ll often see percentages stated as rates of increase or decrease,

which compare growth or decline during a specific period of time to a baseline figure

from an earlier period. Treat these rates cautiously, for unless you know the baseline

number, the rate of increase or decrease is almost meaningless. Think of it this way:

A company that employs two people in the year 2014 and adds an additional employee

mean average of a group of
numbers

median middle number in a
set of numbers arranged in a
ranked order

mode most frequently
occurring number

percentage figure that
shows the relationship
of the part to the whole,
which is represented by the
number 100

rates of increase or
decrease percentage that
uses an earlier baseline
figure to compare growth or
decline

© iStockphoto.com/rook76

In this culture, we think
of numbers as hard data
that tell us how extensive a
problem is and how things
relate to one another.

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