Three American business school professors decided to find out. In a first-of-its-kind study, they analyzed more than 26,000 earnings calls from more than 2,100 public companies over six and a half years using linguistic algorithms similar to the ones employed in the Twitter study. They examined whether the time of day influenced the emotional tenor of these critical conversations — and, as a consequence, perhaps even the price of the company’s stock.

Calls held first thing in the morning turned out to be reasonably upbeat and positive. But as the day progressed, the “tone grew more negative and less resolute.” Around lunchtime, mood rebounded slightly, probably because call participants recharged their mental and emotional batteries, the professors conjectured. But in the afternoon, negativity deepened again, with mood recovering only after the market’s closing bell. Moreover, this pattern held “even after controlling for factors such as industry norms, financial distress, growth opportunities, and the news that companies were reporting.”

In other words, even when the researchers factored in economic news (a slowdown in China that hindered a company’s exports) or firm fundamentals (a company that reported abysmal quarterly earnings), afternoon calls “were more negative, irritable, and combative” than morning calls. Perhaps more important, especially for investors, the time of the call and the subsequent mood it engendered influenced companies’ stock prices. Shares declined in response to negative tone — again, even after adjusting for actual good news or bad news — “leading to temporary stock mispricing for firms hosting earnings calls later in the day.” While the share prices eventually righted themselves, these results are remarkable. As the researchers note, “call participants represent the near embodiment of the idealized homo economicus.”

Both the analysts and the executives know the stakes. It’s not merely the people on the call who are listening. It’s the entire market. The wrong word, a clumsy answer, or an unconvincing response can send a stock’s price spiraling downward, imperiling the company’s prospects and the executives’ paychecks. These hardheaded businesspeople have every incentive to act rationally, and I’m sure they believe they do. But economic rationality is no match for a biological clock forged during a few million years of evolution. Even “sophisticated economic agents acting in real and highly incentivized settings are influenced by diurnal rhythms in the performance of their professional duties.”

Source: When: The Scientific Secrets of Perfect Timing by Daniel H. Pink