Group ideation is the setting for ideation session which is the most well known. It has been popularized with the brainstorming technique where a bunch of people are brought together in a room to find new ideas.

Group ideation is a great tool to create a sense of common goal in a team. Generating ideas feels like a team sport which can make it more fun.

The other advantage of group ideation is when we arrive to the prioritization of ideas. When we have multiple people helping prioritize ideas and define which one have more value we can profit from the knowledge of the crowd.

But there is also a problem with the group ideation process where everyone shares to the group the idea he has. Less ideas, and less different ideas are created. That's something that no many people know but that some research done in the last years tends to show. 

Researchers Brian Mullen, Craig Johnson, and Eduardo Salas published an interesting study in the journal of Basic and Applied Social Psychologyabout group idea generation. The researchers found out something interesting. Individuals will generate more original ideas when they don’t interact with others. To arrive at that finding, the team made a meta-analytic review of over 800 teams.

In my own experience, I come to the exact same conclusion. I have led many idea generation workshops with many different teams. With non-creative professionals, group brainstorming blocked the participants. In one case, we let participants try out group brainstorming versus individual brainstorming. The result was astonishing. When working alone, individuals were able to generate around 10 to 20 ideas in 20 minutes. When working in groups of 4 to 6 people, they were able to produce between 0 and five ideas. The worst team had many discussions but wasn’t able to create a new idea.

You might say that group brainstorming is great. Yes, it avoids that everyone comes up with the same ideas. Yes, group brainstorming is great because you can build on the idea of others. I agree with you, but the problem of group brainstorming is the talking. There is a workaround for that. It’s called silent group brainstorming. Each in the team generates ideas in silence. Each time he has an idea, he writes it down on a post-it and puts it on a shared wall. This common wall is visible for the whole team.