Despite the nearly universal assumption that managers who praise teams help performance and yelling managers hurt it, Social Psychologist Gerben van Kleef and his research team suggested that little research has been done on "how leader emotional displays affect subordinates," and that the results from that research are mixed. The researchers theorized that the effect these emotions had on the team would be changed by the team's "general level of epistemic motivation—that is, the extent to which team members desire to develop and maintain a rich and accurate understanding of situations." People with high levels, for example, would look beyond their own reactions to the manager's emotion to try to understand the meaning behind it.
Van Kleef's study used student teams working on computer tasks that required cooperation. The study focused on anger and happiness precisely because these two strong emotions are evoked in the workplace by team performance. The students completed questionnaires testing their epistemic motivation. (It actually tested their need for structure going into a new situation, but the researchers said this has proven related to epistemic motivation). After a training session and trial run, a remote leader seemed to assess the team's performance via computer. Actually, the assessment was one of two tapes in which the "leader" expressed either happiness or anger through the full range of body language plus a brief phrase at the end. Otherwise the words spoken were exactly the same in both tapes. Then the task was done "for real."
Teams performed better either A) when their members were the type to work at understanding a situation and the boss was angry, or B) when they didn't work at understanding and the boss was happy. Apparently this worked because the high motivation group focused on the reasons the boss was angry—their own poor performance, supposedly—while the low motivation group focused on their own emotions and thus wanted to keep the boss happy. This difference helps explain why previous research on leader emotional displays has provided a range of answers: the effect depends on the audience.
Van Kleef and his team noted that stressful working conditions can reduce epistemic motivation. "Given the current findings, expressing anger would seem unwise in highly taxing conditions." For example, they imply that a manager would want to control himself when a team had an "increasingly high workload close to a deadline…"
Source: Van Kleef, G., et al. (09), "Searing Sentiment or Cold Calculation? The Effects of Leader Emotional Displays on Team Performance Depend on Follower Epistemic Motivation." Academy of Management Journal 22(3):562.