Trials, tribulations, and anecdotes

Aug. 1, 2010
Which do you trust more — published trials, or what you see with your own eyes?

by Bill Landers
[email protected]

Which do you trust more — published trials, or what you see with your own eyes? Even though scientific studies may be much more rigorous and carefully controlled, we usually trust our own observations more. Why are we so willing to trust our own eyewitness observations over clinical trials?

It’s difficult to accept, but eyewitness accounts and recollections are often wrong. We’re not nearly as good observers as we like to think we are. In 1998, Wells et al. studied the first 40 prisoners who were pardoned after DNA tests became available. In 90% of the cases, the sworn eyewitness testimony was wrong.

To test the average person’s power of recollection, Cutler and Penrod (1995) conducted a controlled study in convenience stores. An actor, posing as a customer, would do something unusually memorable, such as paying in pennies. Later, the clerks were asked to identify the actor from mug shots. They were wrong 50% of the time.

Why are our memories so unreliable? The psychologist B.F. Skinner concluded that our mammalian brains just aren’t wired to think deductively. They rely on inductive reasoning.

Deductive reasoning is logical. It utilizes already established facts to determine previously unknown facts. Clinical studies use deductive reasoning. The results of repeated experiments help deduce new information. Here’s a deductive example:

  • Everyone who graduates from hygiene school is a hygienist. [true]
  • Anne graduated from hygiene school. [true]
  • Therefore, Anne is a hygienist. [true]
  • Inductive reasoning is more intuitive but quicker. It assumes that what is already known is universally true.
  • Here’s an inductive example:
  • Every hygienist (who I know) is named Anne. [true]
  • Therefore, all Annes are hygienists [possibly true]. It may be true in your personal experience, but maybe not ... if you knew more people named Anne.
  • An individual’s experience (data set) is just too small to make universal generalizations. Nevertheless, that’s how our brains are wired. Inductive reasoning is a necessary survival trait. Would you stick your hand into a flame? Probably not, but how do you know that you shouldn’t? By repeated experiments? Eventually, you would have enough data to deduce that it will hurt every time, but you’d have a carbonized hand. No, you burned yourself just once and induced that it will hurt every time. The one experience was used to predict every future outcome. That’s how induction works and why we’re wired to think inductively. Anecdotal experience is always inductive because it’s limited to just the things that we know.

Superstitions are inductive. A superstition, by definition, is the belief that something is true when most people believe it’s false. Nevertheless, the superstitious will continue to believe that it is true, because it’s based on their personal experience. And, because it’s true for them, it must (via induction) be true for everyone else as well.

We’re not the only inductively reasoning, superstitious creatures. In 1947, Skinner disovered that caged pigeons are superstitious. They would ritualistically turn clockwise or some other behavior, apparently believing these rituals produced a food pellet — despite the fact that the pellets dropped every 15 minutes regardless.

Are we so different? Don’t we put more “faith” in our own experiences than clinical trials? What we infer from personal experience may be true. But more often, it’s the larger, more rigorous deductive studies that get it right.


Bill Landers has been president of OraTec Corp. since 1992. He is also a leading expert on chairside and laboratory periodontal risk assessment technologies, and his essays on periodontal disease have been published in several dental hygiene journals. Landers is a popular speaker and has presented hundreds of continuing education seminars on the microbiology of periodontal diseases.

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