As in other qualitative research, focus groups do not necessarily need a perfectly representative sample of the participants in the community, since the results will not be generalizable. With that said, you should aim to have a diversity of backgrounds and opinions across your groups in order to get varied perspectives. You might be wondering, how many groups should we conduct in order to do the best focus groups? And how large should the groups be? While there is no one-size-fits-all answer to these questions, there are a few general guidelines you might want to follow.
While some researchers like to do smaller focus groups and others like to do larger groups, the commonly accepted range for the best size is between 6 and 10 participants. Smaller than that and the focus group tends to turn into more of a series of individual interviews, being held at the same time and place. Larger than that and it is difficult to get everyone's opinions in the allotted time. Remember, the key point about focus groups is to see how an issue is discussed in a group dynamic – anything that takes away from group conversation is not a good use of the focus group method.
How many groups should you conduct? Where possible, it is best to have the participants of each focus group matched on an important demographic or other personal characteristic that is relevant to your research question. For instance, you might want to have a group of all women, or a group of all African Americans, a group of people from the same neighborhood, or groups separated by age or language. This helps participants speak more openly and freely, especially when dealing with a sensitive topic.
Get Participatory! When thinking about the types of groups you would like to run a focus group with, it can be very useful to get those folks involved in the research process itself. They can bring a level of insight into the community that you might not have without their participation. This can also cultivate a level of ownership and trust in the research process that can be beneficial for all those involved.
Let's return to the Metamorphosis Project example. We wanted to talk in our focus groups about community problems. We knew from our experience that one of the big problems in the community was conflicts between African Americans and Latinos, especially gang-related conflict. With this in mind, we decided to have different African American groups and Latino groups, as they would likely be more comfortable to speak about this sensitive issue when they were in a more familiar ethnic group. You can see how this could be relevant on a number of topics – if you're talking about health issues, for instance, it might be important to separate by gender. If you're talking about issues of sexual activity, separating by age and by gender might be appropriate.
After you have separated the groups on a relevant characteristic, it is good to conduct at least two focus groups with each section (so, two groups of African Americans and two groups of Latinos). When you conduct only one group, it is hard to know whether that conversation was unique to that group of individuals. By conducting two groups with each, you can look for common themes across the groups when you move onto the analysis stage. Three or four groups with each is even better. Of course, the size and scope of your research sample will depend on your time and resources, so don't worry if you do not meet these guidelines exactly. In addition, you might find that, while you recruited, say, eight people to participate in a group, only four or five showed up! This happens all of the time, so it is often useful to over-recruit by a few people, expecting that some might not show up. You will have to over-recruit by a few extra if you think it might be difficult for some of the participants to make it – for instance, if there is bad weather, traffic, your study population is elderly or ill. Also, any time you can provide some sort of incentive for participating (perhaps a small amount of money or gift card), participants are more likely to attend. Also, providing day-care services during the focus group can be very helpful in recruitment.
How long should the focus group be? The general rule of thumb is no longer than two hours and at least one full hour. Less than that and it is difficult to get a good conversation going. More than that and your participants will be exhausted.