Four Types of Evidence
Dr. Philip N. Howard
University of Washington
An anecdote is one sort of example. How does anecdotal evidence really work? Obviously an anecdote, or another kind of example, cannot prove a general statement, so avoid treating a single case as proving a general point. On the other hand, a single anecdote or counterexample is alone sufficient to disprove a general statement. One successful anecdote will show that one must modify one's claim. An anecdote will not count as weighty evidence, however, either in support of or in opposition to a more limited, narrower claim, which is not intended to apply generally.
2. Testimonial Evidence
In social science communication research, one must (generally) use well-established or credible sources. The testimony of credible persons will sometimes strengthen an argument, but one must almost always say why the reader should especially consider that person's comments. Give credentials. Don't assume, however, that respectable credentials alone establish the fact that we should accept the testimony without question. You should know when experts disagree on an issue, so that one expert's assessment does not alone establish the point. Popular magazines with light reading fare such as Cosmopolitan and People seldom, if ever, provide anything which would strengthen an argument in a research paper. Always give your own comment on a quote or reported view. Don't just report what the authority claims; say why the reader should seriously consider it, and demonstrate your own understanding of it.
3. Statistical Evidence
When you structure part of your argument using statistics, always report the source. Since statistics from different sources may vary or conflict, give reports from multiple sources when possible. Whenever possible, as you report your source, show that it is a reputable one.
4. Analogical Evidence
Analogies provide interest and hopefully illumination to a line of argument. However, you must be cautious when you create your own analogy or evaluate someone else's. The logical power of an analogy is often overestimated. Usually an analogy will help a person understand a relation and see new connections between things, but seldom does it provide hard proof of a conclusion or thesis for a person who ardently resists that view. Analogies are especially useful for articulating a new perspective that has just beensupported by empirical evidence, because they often illustrate rather than establish points of view.
Adapted from Seech, Z. (1993). Writing philosophy papers. Belmont, Calif.: Wadsworth Pub. Co.