The following is a modified excerpt from Applied Qualitative Research Design: A Total Quality Framework Approach (Roller & Lavrakas, 2015, pp. 130-131).

Qualitative researchers are routinely faced with the decision of how many in-depth interviews (IDIs) or focus group discussions to conduct. This decision often revolves around time-cost-benefit trade-off considerations fueled by the tension between neither wanting to conduct too many nor too few IDIs or focus groups.

When it comes to the focus group method, the decision of how many group discussions to conduct is based on any number of factors and will vary depending on the situation for each study.  However, a few of the critical factors that the prudent researcher will think about when considering the number of discussions at the outset for any focus group study are the:

• Geographic range of the target population, e.g., whether the target population for in-person groups is located in one city or spread across the U.S.
• Depth of the discussions, i.e., the number of topics/issues and questions expected to be covered to satisfy research objectives. For example, fewer group discussions may be necessary if the primary research objective is to learn mothers’ preferences for shelf-stable baby food, while a greater number of groups may be needed if the objective is to understand mothers’ preferences across all types of baby food and, specifically, to investigate the priority they place on nutritional and organic foods.
• Homogeneity or heterogeneity of the group participants. Using the example above, more groups will be required if the mothers of interest range in age from 25-40 years as well as in income level and if there is reason to believe that attitudes and behavior vary across these demographic characteristics.
• Variation in results that is expected to occur across the different focus groups that will be conducted. If there is little variation expected from one group to another (e.g., if group participants are highly homogeneous, or the attitudes among participants in New York are not expected to be different than those in Dallas), then only a few focus groups may suffice.  If there is a great deal of variation expected, then many focus groups will be required to fully measure the range of experiences, attitudes, and knowledge the participants will have to impart in the discussions.
• Project schedule and amount of available time to complete the study.
• Research budget that is available to fund the study.

It is this assortment of factors that cause qualitative researchers to generally disagree on the optimal number of focus groups. Krueger and Casey (2009, p. 21) state that “the accepted rule of thumb is to plan three or four focus groups with each type or category of individual.” Kitzinger (1994) and her colleagues conducted 52 group discussions concerning the media coverage of AIDS among broad, diverse population groups across England, Scotland, and Wales; and Peek and Fothergill (2009) reported conducting 23 discussions with Muslim American students due, in part, to the need to segment groups by gender. Yet others, such as McLafferty (2004) use the concept of saturation (i.e., conducting group discussions only to the point when no new information is being gleaned) as their “guiding principle” when determining if the appropriate number of groups have been conducted.

Although the considerations listed above may assist the researcher during the research design phase to establish the number of groups to conduct, it does little to help evaluate the set-upon number when in the field. To be clear, it can be expensive and disruptive to the research process to cancel or add group sessions to a focus group study that is underway (particularly, when conducting in-person discussions that require reserving and making arrangements with brick-and-mortar facilities); however, it is important for the focus group researcher to assess all the components of his or her research design – including the number of group discussions – throughout the process.

The question of how many group discussions to conduct raises a host of issues associated with data quality.  Similar to IDIs^*, the researcher’s assessment of the number of focus groups to conduct while in the field goes way beyond the concept of data saturation and takes into account quality concerns such as the degree to which:

• All key constructs have been covered in all discussions.
• The moderator clearly understands the feedback and responses obtained in each discussion.
• Research objectives have been met.
• Variations in the data can be explained.
• Reflection reveals that the moderator maintained objectivity throughout all discussions.
• The data inform the subject matter.
• Triangulation confirms or denies the researcher’s initial hypotheses.
• The discussions have divulged a story that explains the research question for each of the population segments or sub-groups.
• Opportunities for further research have emerged from the discussions.

An important additional component to this assessment, that is unlike that for IDIs, is the interactivity or group dynamics within the discussions.  Specifically, the researcher needs to carefully consider the degree to which participants in all groups equally shared their experiences and thoughts during the discussions.  If, for instance, one or more focus groups were dominated by a small number of participants who were outspoken on the issues, the researcher should be cautious when assessing the value of these discussion groups (in terms of the credibility of measurement) and consider these dominant-participant groups in the determination of the number of groups to conduct.

^* See “Designing a Quality In-depth Interview Study: How Many Interviews Are Enough?”

Krueger, R. A., & Casey, M. A. (2009). Focus groups (4th ed.). Thousand Oaks, CA: Sage Publications.

Kitzinger, J. (1994). The methodology of focus groups: The importance of interaction between participants. Sociology of Health & Illness, 16(1), 103–121.

Peek, L., & Fothergill, A. (2009). Using focus groups: Lessons from studying daycare centers, 9/11, and Hurricane Katrina. Qualitative Research, 9(1), 31–59.

McLafferty, I. (2004). Focus group interviews as a data collecting strategy. Journal of Advanced Nursing, 48(2), 187–194.

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