What’s the most convincing type of evidence?
Evidence is factual statements (or perceived to be factual) offered in support of the speaker’s claim. There are, generally, three kinds of evidence – statistical, causal and anecdotal.
‘Statistical’ is numerical summaries of many instances. ‘Causal’ provides an explanation for an occurrence in which I’ll also include “expert opinion”. ‘Anecdotes’ are from specific instances. I’ve already mentioned why anecdotes are problematic.
Considering evidence isn’t simple. There are many variables involved including who presents it, what situation it is presented in, our political slant and personal values.
Causal evidence, especially that given to you by a knowledgeable person or professional, can be sufficient for typical needs. Your dentist tells you why you have a problem with your teeth, your doctor tells you what illness is affecting you, or you hair stylist tells you why your hair went a funny color. You trust this person, the reasoning makes sense, so you understand and accept it. In most cases, that’s just fine for your purposes.
Statistical evidence is not as engaging. It’s a lot of numbers that may not register right away. Humans are notoriously poor at dealing with odds, significance and risk management. Statistically, people are more likely to die in a car crash than a plane wreck. Yet many people fear planes beyond reason. It’s hard to deal with numbers when there are other emotional or cultural factors at play.
But, if statistical evidence is presented in a vivid way, it can strongly affect peoples’ understanding and opinion on a subject. We see science news presented in this way by very few publications or media outlets. The New York Times science writers immediately come to mind.
Anecdotes are most of what we are given by the news media, talk shows and social interactions. Contrary to what we might assume, research shows anecdotes are not actually the most convincing kind of evidence. Even though they are emotionally engaging and feed into people’s presuppositions, it could be that we actually realize that when an important decision is to be made, more substance is required. When dealing with a serious medical issue, deciding on a neighborhood to live in or which job to take, we don’t rely on anecdotes as much but we seek out those other kinds of evidence and science-based results. Anecdotes are useful in supporting the other forms of evidence but aren’t reliable as the sole means of evidence.
Anecdotes are actually the least persuasive type of evidence when we control for the quality called “vividness”. Vivid presentations are more mentally engaging than numbers. They are more easily recalled in memory as imagery. If statistical or causal evidence is made more vivid, it can be just as persuasive as anecdotal.
Causal evidence is particularly good at changing faulty beliefs, people can build a new mental model of how things really work. That is, only if they are willing to changing their mind in the first place. Statistical evidence, made more vivid of course, can be immediately persuasive and remain so in the long-term.
That’s a positive note for the reality-based community. We just have to figure out how to be compelling as the dramatic purveyors of nonsense. We would use strong evidence in a meaningful way rather than the weak and weaselly (or false) “facts” pseudoscientists sell by saying, “I know this is true, because I’ve seen it work.”
Baesler, E.J., J.K. Burgoon (1994) “The Temporal Effects of Story and Statistical Evidence on Belief Change”, Communication Research 21(5) pp. 582-602.
Hoeken, H. (2001) “Anecdotal, Statistical, and Causal Evidence: Their Perceived and Actual Persuasiveness” Argumentation 15 p. 425–437.
Hornikx, J. (2005) “A review of experimental research on the relative persuasiveness of anecdotal, statistical, causal, and expert evidence”, Studies in Communication Sciences 5(1), pp. 205-216.
Kazoleas, D.C. (1993). “A comparison of the persuasive effectiveness of qualitative versus quantitative evidence: A test of explanatory hypotheses’”, Communication Quarterly, 41 (1), pp. 40-50.
Moore, A. and J. Stilgoe (2009), “Experts and Anecdotes: The Role of “Anecdotal Evidence” in Public Scientific Controversies”. Science, Technology & Human Values 34(5) p. 654-677.