A company is developing a new breakfast cereal. Before launching it, they invite eight people to a room, give them samples, and ask what they think. The discussion is recorded. A moderator guides the conversation. That is a focus group: a small group of people whose reactions are studied to gather qualitative feedback on a product, service, or idea.

Focus groups are used in marketing, product development, and political research. They are good at generating ideas and uncovering attitudes that surveys miss. A survey can tell you that 60 percent of people prefer a sweeter cereal. A focus group can tell you why, and what language people use to describe what they want. The dynamic of group discussion can surface opinions that individuals would not express alone.

The method has drawbacks. A dominant personality can steer the conversation. People may say what they think the moderator wants to hear. The sample is small, so the findings are not statistically representative. Focus groups are best used alongside other methods, not as a substitute for quantitative research. They tell you what people think and why. They do not tell you how many people think it.