Everyone’s experienced the man in the bar who is absolutely, positively sure that he is right, beyond all measure of reason or debate. This experience is well known to women, as we live in a culture of rampant mansplaining. If you weren’t convinced, there is now a scientific study that specifically links testosterone in men to over-confidence and poor decision making.

Conducted by Caltech, the Wharton School, Western University, and ZRT Laboratory, the study, which will be published in an upcoming issue of Psychological Science, reports that higher levels of testosterone increase the male tendency to rely on intuitive judgments and negate cognitive reflection. In other words, act now and ask questions later — or just not at all.

The study included 243 males and is one of the largest of its type ever conducted. Participants were given a dose of testosterone gel or placebo gel before taking a cognitive reflection test. The men given testosterone scored significantly lower than the placebo group, on average by as much as 20 percent. They also found that participants given testosterone gave their correct answers more slowly than those given the placebo.

Baseball bats

An example of one of the cognitive test questions was:

A bat and a ball cost $1.10 in total. The bat costs $1.00 more than the ball. How much does the ball cost?

The instinctive answer is that the ball costs 90 cents, but that’s wrong. In order for the bat to cost $1.00 more, the ball has to cost 5 cents (the bat costs $1.05).

“What we found was the testosterone group was quicker to make snap judgments on brain teasers where your initial guess is usually wrong,” says Caltech’s Colin Camerer, a professor of behavioral economics. “The testosterone is either inhibiting the process of mentally checking your work or increasing the intuitive feeling that ‘I’m definitely right.’”

The researchers believe that the results prove there is a link between the effect of testosterone and an increase in confidence. “We think it works through confidence enhancement. If you’re more confident, you’ll feel like you’re right and will not have enough self-doubt to correct mistakes,” Camerer says.


The sex steroid testosterone regulates reproductive behaviors such as intra-male fighting and mating in non-humans. Correlational studies have linked testosterone with aggression and disorders associated with poor impulse control, but the neuropsychological processes at work are poorly understood. Building on a dual-process framework, we propose a mechanism underlying testosterone’s behavioral effects in humans: reducing cognitive reflection. In the largest behavioral testosterone administration study to date, 243 men received either testosterone or placebo and took the Cognitive Reflection Test (CRT), that estimated their capacity to override incorrect intuitive judgments with deliberate correct responses. Testosterone administration reduced CRT scores. The effect was robust to controlling for age, mood, math skills, treatment expectancy and 14 other hormones, and held for each of the CRT questions in isolation. Our findings suggest a mechanism underlying testosterone’s diverse effects on humans’ judgments and decision-making, and provide novel, clear and testable predictions.

Read the full study (PDF).

Photos via Flickr / PMillera4, Giphy