By Dr. Ken Broda Bahm:
The rooster can’t take credit for the sunrise. While the crowing tends to occur just before dawn, it does not cause the sun to come up. Thinking that “A” then “B” means that “A” caused “B” is a well-known logical mistake and fallacy. In Latin, it goes by the name post hoc ergo propter hoc, meaning “after this, therefore because of this.” That kind of reasoning is also studied as a cognitive bias – the “illusion of causality” – and a long line of research shows that it is a very powerful illusion. Practical experience confirms that as well. In a recent article in FiveThirtyEight, Christie Aschwanden shares the story of a pediatrician who was about to inject a child with a vaccination when the child suffered a seizure. It occurred to the pediatrician that if he had given the shot a moment earlier, the parents would have been dead certain that the vaccine caused the seizure and “no study in the world would have convinced the parent otherwise.”
The FiveThirtyEight piece covers new research showing that this illusion of causality doesn’t just prime us to accept mistaken causal links, it also makes us more resistent to new information that would correct those mistakes. Causation, of course, is often a central issue in litigation. Causal conclusions matter not only in the use of research (for instance, in a products case tying a drug or a device to good or bad outcomes), it also matters more basically when jurors decide whether the defendant’s liability is what caused damage to the plaintiff. The tendency to think that “negligence occurred,” for example, and “then the damage occurred,” can lure jurors and other legal fact-finders to skip over the more analytical consideration of causation. This post takes a look at the recent research, and also shares some ideas on teaching jurors to resist the lure of post-hoc thinking.
The Research: The Illusion of Causality Breeds Resistance to New Information
An Australian and Spanish research team (Yarritu, Matute, & Luque, 2015) published a recent article in the British Journal of Psychology. The background, research and results are further explained in the FiveThirtyEight piece, and in great detail in the article itself. But let me provide a quick thumbnail here.
In the first phase of the study, the team presented research participants with a series of 100 cases in which a patient is either given a medicine or not, and then the patient either recovers or not. At the end, the research participant gives an opinion on whether the drug worked. In reality, the drug is a placebo, and the recovery rate is 70 percent whether the drug is given or not. Participants were, however, placed in two conditions designed to manipulate their perception of the placebo’s effectiveness: In the “high illusion” condition, the drug was given 80 percent of the time, while in the “low illusion” condition, the drug was only given 20 percent of the time. In both groups, the success rate remained 70 percent whether the drug was given or not. But as expected, those in the “high illusion” group who were given more opportunities to see the coincidental “drug then recovery” sequence were more likely to develop the belief that the drug worked.
Then the researchers decided to mix things up a bit for the second phase. Both goups, including the same participants, took another run at the case-review process, only this time with two drugs being given to the patient. One was the same ineffective drug from phase one, and the other was a drug that actually was strongly associated with patient recovery. The information for both groups was the same this time, but because the “high illusion” group had already formed a belief about the placebo’s effectiveness from phase one, they were less likely to see any benefit from the effective drug. Instead, they attributed any advantage to the placebo. The low illusion group got it, but the high illusion group did not.
Discouraging Post Hoc Thinking:
In trial, sometimes post-hoc thinking helps your side. For plaintiffs, for example, it is a benefit to not have to worry too much about causality if there is a strong liability case and a strong damages case. For those times, however, when you want your fact-finders to be a bit skeptical about a relationship that might invite “the illusion of causality” on its surface,” (for example, when your drug was taken, then the patient had a heart attack), let me suggest a few simple rules for inviting greater scrutiny.
Teach Fully
Research also shows, thankfully, that a little bit of knowledge can train people away from the illusion of causality. In a study that is also covered in the FiveThirtyEight piece, another team (Barberia, 2013) found that teaching about the causal illusion — pointing out holes, as well as information on the basic components of the scientific method, like a baseline measurement or a control group — can significantly decrease susceptibility to post-hoc reasoning.
Teach Early
Remember the 2015 study, however, shows that once set, causal beliefs are difficult to change. For that reason, you should begin educating jurors about causation as early as possible, ideally in voir dire. Ask jurors about their knowledge and beliefs about roosters and sunrises, about control groups and baselines, and you will probably find at least one juror who is willing to educate the rest of the group on the basics.
But Don’t Neglect the Story
This final reminder is an important one. Even with an education on logical traps, jurors (and judges, experts, and counsel as well) will still lean toward what they want to be true. So address those motivations by telling a compelling story. The conclusion of Christie Aschwanden’s FiveThirtyEight article is worth quoting at length:
“Explaining the science and helping people understand it are only the first steps. If you want someone to accept information that contradicts what they already know, you have to find a story they can buy into. That requires bridging the narrative they’ve already constructed to a new one that is both true and allows them to remain the kind of person they believe themselves to be.”
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Other Posts on Causation:
- Mind the Gap: Stop Jurors From Jumping Straight From Liability to Damages
- Help Your Fact Finders Think About What Might Have Been
- Think Your Jury Understands Probability? Don’t Bet on It
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Barberia, I., Blanco, F., Cubillas, C. P., & Matute, H. (2013). Implementation and assessment of an intervention to debias adolescents against causal illusions. PloS one, 8(8), e71303.
Yarritu, I., Matute, H., & Luque, D. (2015). The dark side of cognitive illusions: When an illusory belief interferes with the acquisition of evidence?based knowledge. British Journal of Psychology.
Image Credit: 123rf.com, used under license.