You have probably read articles that reference the famous Linda Study conducted by researchers Daniel Kahneman and Amos Tversky back in the early 1970’s. In it, the researchers describe an outspoken person named Linda who is and smart and politically active and who has participated in anti-nuclear demonstrations. They then ask the subject to indicate whether Linda is more likely to be a) a bank teller or b) a bank teller who is also an active feminist.

No direct evidence is given to indicate that Linda is either a bank teller or a feminist. She is smart so she might be a bank teller, and since she has been socially active she might be a feminist. But logically it is far more likely that Linda is only one of these things than that she is both. Yet most people, given the choices presented and regardless of education, answer that Linda is probably both a bank teller and a feminist. This is an example of the Conjunction Fallacy (see here), in which a person mistakenly believes that multiple conditions are more likely than a single one.

Although this study is frequently cited in popular science articles, the conclusions drawn from it have been strongly criticized or at least given more nuanced analysis (see here). Few popular ideas from science since the Heisenberg Uncertainty Principle have been so misused and overextended as the Linda Study. We really should stop reading so much into this study and cease abusing it so badly.

An example of one such popular science article describes research by Professor Keith Stanovich (see here). In his work he used the Linda Study methodology along with other tests to measure rationality. Although I do not know how well this popular science article represents the actual research by Stanovich, it suggests that the Linda Test is a strong indicator of rationality. I find that assertion very troubling.

First off, while the Linda Test does expose the Conjunction Fallacy, we are all are susceptible to a huge number of logical fallacies. I document dozens of these in my book, “Belief in Science and the Science of Belief” (see here). While everyone should be taught to do better at recognizing and avoiding logical fallacies, failing to do so probably does not adequately correlate to irrational thinking.

If subjects were made aware that this was intended as an SAT-style logic gotcha, many would answer it in a more literal context. But we normally assume a broader scope of inference when answering this sort of question and the pattern-recognition machines we call our brains are capable of all sorts of fuzzy logic that is completely independent of, and much broader than, strict mathematical logic. In the real world, it might well turn out that women like Linda are in fact more likely to be both bankers and feminists.  Moreover “both” is a far richer answer in the context of most real-world interactions. The more logically correct answer is less insightful and interesting.

This is not to suggest that we should become lax about adhering to principles of logic, but only to suggest that a simple “brain teaser” logic question is not a very powerful indicator of overall rationality. Furthermore, equating rationality to a fallacy recognition test diminishes the profound complexity and importance of rationality.

I suggest that there are far stronger indicators of rationality. Does the subject believe in God? Do they deny climate-change? Do they subscribe to pseudoscientific nonsense? Is their thinking muddled by irrational New Age rationalizations? Do they insist the world is only 6 million years old and that humans coexisted with dinosaurs (cough) Ken Ham see here (cough).

Here’s the problem. All of these direct indicators are too entrenched and widespread to be overtly linked to irrationality. So instead we use safe, bland, non-confrontational indicators like the Linda Test that are at best weak and at worst undermine important and frank questions about rationality.

So dump Linda already in favor of far more meaningful measures of rationality!