Page 417 - Between One and Many The Art and Science of Public Speaking

384 Part 4 Contexts for Public Speaking

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50 years of research on the persuasive effects of evidence. Unlike many previ-
ous researchers, Reinard did not rely solely on the conclusions of other studies;
he went back to the original works and reinterpreted the data using comparable
defi nitions. He found that the research was surprisingly consistent. Further, he
found that evidence, under most conditions, did in fact enhance the likelihood
of persuasive effects. As Reinard writes, “After fi fty years of research on the per-
suasive effects of evidence, the claims for the persuasiveness of evidence emerge
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as quite strong.” Some of his most important fi ndings follow. 9
Testimonial assertions (the judgment and opinions of people other than the per-
suader) are most effective when the sources are identifi ed and their qualifi ca-
tions explained to receivers. Mere “name-dropping” has not been found to be
persuasive.
Reports (factual information that describes events as seen by either partici-
pants or observers) are persuasive, especially when they are believable, specifi c,
and the receivers are intelligent. It is also important that the reporter’s qualifi ca-
tions be explained for receivers.
Statistics, somewhat surprisingly, tend not to be very persuasive in the short
term although results are better in the long term. To be most effective, statistics
should be preceded by a specifi c example, which is then shown to be representa-
tive through the use of statistics. To be persuasive, it is also important to explain
how statistics were gathered. Research has demonstrated that when examples
and personal anecdotes confl ict with statistics, people are more likely to be per-
suaded by the examples.
Source credibility–that is, the believability of the person delivering a persuasive
message–has an important relationship to the persuasiveness of evidence. Us-
ing evidence tends to build a persuader’s credibility. However, a source that is
already highly credible is not likely to become more persuasive through the use
of evidence in the short term (although long-term persuasiveness is enhanced).
This is because of a ceiling effect, which means the persuader has already reached
the maximum persuasive potential through his or her source credibility. With or
without evidence, the persuader cannot become more persuasive.
Although the mode of presentation (video, tape, live, etc.) doesn’t seem to
make any difference, a poorly delivered presentation will not be persuasive no
matter how good the evidence.
One very consistent research fi nding is that the most persuasive evidence
comes from highly credible sources, found to be believable by receivers. The
overall fi nding of the body of research is that high-quality evidence is more per-
suasive than low-quality evidence, especially for receivers who have a personal
stake in the issue, who are trained in reasoning, who fi nd the topic novel, who
are not biased about the issue, and who have attended college.
fi rst-order data Technically, there are three types of evidence. They are called fi rst-, second-,
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Evidence based on and third-order data. First-order data is evidence based on personal expe-
personal experience. rience. When a person whose life was turned around by education speaks to a
high school audience about staying in school, this is fi rst-order data. It not only
second-order data
carries with it logical force but also helps enhance the credibility of the speaker.
Evidence based on
Second-order data is evidence based on expert testimony. When those who
expert testimony.
debate the research on global warming cite professors, public offi cials, and other
experts on the subject, they are presenting the audience with second-order data.
third-order data
Third-order data is evidence based on facts and statistics. The number of
Evidence based on facts
teen pregnancies each year and the percentage of teenagers having unprotected
and statistics.
sex are examples of third-order data.