384 17.2 Using PersUasive strategies
who is known to be unbiased, fair, and accurate. If the U.S. Surgeon General
has expressed an opinion regarding drug testing, his or her opinion would
be helpful evidence. Even so, opinions are usually most persuasive if they
are combined with other evidence, such as facts or statistics that support the
expert’s position.statIstICs A statistic is a number that is used to summarize several facts or
samples. In an award-winning speech, Jeffrey Jamison used statistics effectively
to document the serious problem of alkaline batteries polluting the environment.
He cited evidence from The New York Times documenting that “—each year we
are adding 150 tons of mercury, 130 tons of lead, and 170 tons of cadmium to
the environment.”^12 Without these statistics, Jeffrey’s claim that alkaline batter-
ies are detrimental to the environment would not have been as potent. Again,
you may want to review the discussion on the appropriate use of statistics in
Chapter 8.
Does the type of evidence you use make a difference in whether your
listeners will support your ideas? One research study found that examples
and illustrations go a long way in helping to persuade listeners.^13 Additional
research documents the clear power of statistical evidence to persuade.^14 And
yet another research study concluded that using both statistics and specific
examples is especially effective in persuading listeners.^15 Poignant examples
may touch listeners’ hearts, but statistical evidence appeals to their intellect.Using Evidence Effectively
We’ve identified what evidence is and why it’s important to use evidence to sup-
port your conclusions. But what are the strategies for using evidence effectively?
Here are a few suggestions.^16use CreDIble evIDenCe Your listeners are more likely to respond to your
arguments when they believe the evidence you use is credible—from a trustwor-
thy, knowledgeable, and unbiased source. Remember, it’s the listener, not you,
who determines whether the evidence is credible.
One type of evidence that is especially powerful is reluctant testimony, a
statement by someone who has reversed his or her position on a given issue, or
a statement that is not in the speaker’s best interest. For example, at one point
the owner of a large construction company, who wanted the contract to build
a new dam, was in favor of building the new dam to create a water reservoir.
But after further thought, he changed his mind and now is against building the
dam. The reluctant testimony of that construction company owner would bol-
ster your argument that the dam is a financial boondoggle. Reluctant testimony
is especially effective with a skeptical audience; it demonstrates how another
person has changed his or her mind and implicitly suggests that listeners should
do the same.^17