As I have noted in previous articles, we as human beings tend to grossly overestimate our ability to make decisions. Most of us like to believe that our intellect, our experiences, and our perceived expertise lead us to make rational and well-informed decisions. However, decades of research paint a much different picture. As it turns out – irrespective of our intellectual ability – human beings are highly irrational decision-makers. As it turns out, our judgments of situations and of other people are typically based not on systemic data, but on very limited personal experiences.
Among the many ways in which we engage in irrational decision making, one of the most insidious involves committing what is known as the base rate fallacy (or the base rate effect, as it is commonly referred to among social scientists). This is – in layperson terms – the tendency to ignore systemic data regarding prevalence (or base rate probability) in favor of general information that is usually based on limited personal experience. There are two primary ways that this fallacy manifests itself, and for an examination, we shall turn to the work of Daniel Kahneman and Amos Tversky.
In one of the most important programs of research to emerge from the social sciences, Kahneman and Tversky showed that rather than making judgments based on systemic data, we as humans tend to rely on two heuristics: the representativeness heuristic and the availability heuristic. For an example of the representativeness heuristic, let’s say that the prevalence of a certain cancer-like disease is 2 percent among the general population. And let’s assume that a patient visits a doctor’s office, complaining of fatigue, nausea, and odd bruising – all symptoms of this disease. In succumbing to the representativeness heuristic, the doctor may erroneously conclude that this particular patient has a 90 percent probability of having this disease, given that the symptoms are highly representative of this disease. In reality, the actual probability is (for all intents and purposes) equal to the prevalence (base) rate.
For an example of the availability heuristic, consider that many folks, since the events of September 11th, have resisted air travel and opted for other mean of (more dangerous) transportation, even though those decisions are statistically irrational. However, because the events of September 11th are salient and most-readily come to mind (i.e., are most available to memory), folks tend to grossly overestimate the probability that such a horrific event will occur once again.
Unfortunately, we have a very recent example of the base rate fallacy at play. After the gruesome and unfathomable murders of children and school officials at Sandy Hook Elementary School, the nation was in a collective state of shock and mourning. Even more unfortunately, many individuals chose this event as fodder to proselytize for various political causes, or to angrily spew forth talking points. It is a natural tendency for humans to attempt and identify one singular, root cause for unimaginable tragedy, which often results in the creation of moral panic rather than logical solutions. And out of this attempt to find a root cause, individuals with mental illness became targets of erroneous judgments.
If you were to poll most folks in this country, they will grossly overestimate the likelihood that any given person with a mental illness will also have violent tendencies (this is a finding that predates the shootings). As a result, after the shooting last month, there were many calls for more stringent psychological evaluations and testing for mental illness, and not just for those who wanted to legally purchase firearms. Sadly, these calls only further perpetuated the stigma that haunts the mentally ill throughout the country.
In reality, folks with a mental illness are no more likely to commit a violent crime than any individual amongst the general population. Even for an illness like Schizophrenia of the paranoid type, which many individuals believe to be closely and significantly associated with the propensity to commit violent crime, the actual prevalence rate of violence is no greater when compared to the general population. In fact, individuals suffering from this subtype of schizophrenia are typically quite the opposite of violent – they are instead fearful and reclusive. In short, the existence of mental illness is a very poor predictor of future violent behavior.
What can result are policies that (A) are ineffective; and (B) are potentially harmful. First, these policies can seek to address “risk factors” that aren’t really risk factors at all. Second, specific groups of people can be unfairly targeted as threats to society, when the data clearly shows otherwise (this is the very foundation of a moral panic). In the case of the mentally ill, that growing stigma only further decreases the likelihood that individuals will seek proper treatment, out of a fear of being labeled as a risk to society.