From the article:
The study, which is one of the largest of its type ever conducted, included 243 males who were randomly selected to receive a dose of testosterone gel or placebo gel before taking a cognitive reflection test. A math task was also given to control for participant engagement, motivation level, and basic math skills.
The questions included on the cognitive reflection test are exemplified by the following: A bat and a ball cost $1.10 in total. The bat costs $1 more than the ball. How much does the ball cost?
[…]
The results show that the group that received testosterone scored significantly lower than the group that received the placebo, on average answering 20 percent fewer questions correctly. The testosterone group also “gave incorrect answers more quickly, and correct answers more slowly than the placebo group,” the authors write. The same effect was not seen in the results of the basic math tests administered to both groups. The results “demonstrate a clear and robust causal effect of [testosterone] on human cognition and decision-making,” they conclude.
The researchers believe that the phenomenon they’ve observed can be linked to testosterone’s effect of increasing confidence in humans. Testosterone is thought to generally enhance the male drive for social status, and recent studies have shown that confidence enhances status.
“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.