01 You might realize a certain bias regarding focus groups in this text. Here’s why: “Focus groups are actually contraindicated by important insights from several disciplines,” says Gerald Zaltman, Emeritus Professor, Harvard Business School. “The correlation between stated intent and actual behavior is usually low and negative.” Source: Zaltman, G. (2003). How Customers Think: Essential Insights into the Mind of the Market. Harvard Business Press, p. 122.
02 A control group is often used in experiments: one group receives a specific treatment, while the other group, the control group, receives no treatment or the standard treatment.
03 See #TiSDD chapter 10, Facilitating workshops, for a detailed description of how to establish a safe space in a workshop.
With a focus group, researchers strive to understand the perceptions, opinions, ideas, or attitudes toward a given topic. Focus groups are mostly carried out in a rather informal setting, like a meeting room or a special room where researchers observe the situation in a non-participant manner through a one-way mirror, or via live video coverage in another room. The aim is that participants feel free to discuss the given topics from their own perspective. 
Researchers often ask only an initial question and then observe the group discussion and dynamics. Sometimes a researcher acts as a moderator, guiding the group through a set of questions. In a dual-moderator focus group one researcher facilitates the process while the other observes interactions between the participants. In contrast to co-creative workshops, researchers do not act as facilitators and the participants do not work with boundary objects in order to create an outcome together.
Although focus groups are often used in business, they have only limited applicability in service design. They are not useful when we need to understand existing experiences in context as they are done in a lab setting without a situational context. Unlike co-creative workshops, focus groups usually do not use boundary objects the group can work on together, such as personas, journey maps, or system maps. This often leads to limited informative value as results depend on the moderated discussion. Therefore, moderators need to take care to avoid results that are biased by issues like observer effect, group think, or social desirability bias, to name but a few.