A recent episode of This American Life interviewed Will Felps, a professor who conducted a sociological experiment demonstrating the surprisingly powerful effect of bad apples.

Groups of four college students were organized into teams and given a task to complete some basic management decisions in 45 minutes. To motivate the teams, they're told that whichever team performs best will be awarded $100 per person. What they don't know, however, is that in some of the groups, the fourth member of their team isn't a student. He's an actor hired to play a bad apple, one of these personality types:

• The Depressive Pessimist will complain that the task that they're doing isn't enjoyable, and make statements doubting the group's ability to succeed.
• The Jerk will say that other people's ideas are not adequate, but will offer no alternatives himself. He'll say "you guys need to listen to the expert: me."
• The Slacker will say "whatever", and "I really don't care."

The conventional wisdom in the research on this sort of thing is that none of this should have had much effect on the group at all. Groups are powerful. Group dynamics are powerful. And so groups dominate individuals, not the other way around. There's tons of research, going back decades, demonstrating that people conform to group values and norms.

But Will found the opposite.

Invariably, groups that had the bad apple would perform worse. And this despite the fact that were people in some groups that were very talented, very smart, very likeable. Felps found that the bad apple's behavior had a profound effect – groups with bad apples performed 30 to 40 percent worse than other groups. On teams with the bad apple, people would argue and fight, they didn't share relevant information, they communicated less.

Even worse, other team members began to take on the bad apple's characteristics. When the bad apple was a jerk, other team members would begin acting like a jerk. When he was a slacker, they began to slack, too. And they wouldn't act this way just in response to the bad apple. They'd act this way to each other, in sort of a spillover effect.

What they found, in short, is that the worst team member is the best predictor of how any team performs. It doesn't seem to matter how great the best member is, or what the average member of the group is like. It all comes down to what your worst team member is like. The teams with the worst person performed the poorest.

The actual text of the study (pdf) is available if you're interested. However, I highly recommend listening to the first 11 minutes of the This American Life show. It's a fascinating, highly compelling recap of the study results. I've summarized, but I can't really do it justice without transcribing it all here.

Ira Glass, the host of This American Life, found Felps' results so striking that he began to question his own teamwork:

I've really been struck at how common bad apples are. Truthfully, I've been kind of haunted by my conversation with Will Felps. Hearing about his research, you realize just how easy it is to poison any group [...] each of us have had moments this week where we wonder if we, unwittingly, have become the bad apples in our group.

As always, self-awareness is the first step. If you can't tell who the bad apple is in your group, it might be you. Consider your own behavior on your own team – are you slipping into any of these negative bad apple behavior patterns, even in a small way?

But there was a solitary glimmer of hope in the study, one particular group that bucked the trend:

There was one group that performed really well, despite the bad apple. There was just one guy, who was a particularly good leader. And what he would do is ask questions, he would engage all the team members, and diffuse conflicts. I found out later that he's actually the son of a diplomat. His father is a diplomat from some South American country. He had this amazing diplomatic ability to diffuse the conflict that normally would emerge when our actor, Nick, would display all this jerk behavior.

This apparently led Will to his next research project: can a group leader change the dynamics and performance of a group by going around and asking questions, soliciting everyone's opinions, and making sure everyone is heard?

While it's depressing to learn that a group can be so powerfully affected by the worst tendencies of a single member, it's heartening to know that a skilled leader, if you're lucky enough to have one, can intervene and potentially control the situation.

Still, the obvious solution is to address the problem at its source: get rid of the bad apple.

Even if it's you.