You are faced with a decision: bring participants together in one room and observe their opinions clash, or invite them individually and delve deeper into their motivations? The choice between FGI and IDI in qualitative research is not a matter of preference or budget, but of matching the technique to what you genuinely want to discover. The wrong decision at this stage can block access to the most valuable insights before the first respondent even appears.<\/p>\n
Focus group interview (FGI) and in-depth interview (IDI) are two core qualitative methods that differ not only in the number of participants, but above all in their underlying logic of inquiry. FGI relies on group dynamics: it reveals social norms, the language used to describe categories, responses to stimuli, and how people negotiate meanings in the presence of others. IDI, in turn, provides access to an individual narrative – a decision-making journey, emotions, and experiences that are difficult to articulate in a group.<\/p>\n
The question of “when FGI” most often comes down to three situations: testing concepts (advertising, product, or packaging concepts), exploring a category and consumer language, and researching areas where an exchange of views between participants enriches the data. IDI works well where the topic is sensitive (health, finances, relationships), where the respondent represents a rare group (B2B decision-makers, specialist physicians), or where the aim is to reconstruct a complex decision-making process that cannot easily be recreated in a group discussion.<\/p>\n
The FGI vs. IDI decision in research should stem from a working hypothesis, not organizational preferences. If the question begins with “how do people talk about…”, “what associations does … evoke?”, or “which version of the concept generates the strongest response?” – this is the territory of focus group interviews. If it is phrased as “why did this person make decision X?”, “what did the full purchase journey look like?”, or “what lies behind discontinuing the service?” – an in-depth interview is the appropriate method.<\/p>\n
In Hume’s Institute projects, the greatest risk of error is observed not at the implementation stage, but during briefing – when the client’s business objective has not been translated into a research question that clearly indicates the appropriate technique. This is why the starting point is always to distinguish whether the aim is to capture group responses or map an individual’s world of meanings.<\/p>\n
In practice, method selection is based on several criteria that should be analyzed before choosing a research provider:<\/p>\n
As Hume’s Institute experts point out, the choice between FGI and IDI begins with the question: what do we want to discover – group dynamics or an individual’s world of meanings? This distinction structures the entire project, from the discussion guide and recruitment through to the way transcripts are analyzed. An FGI discussion guide must anticipate moments when opinions are confronted and include techniques that engage the group; an IDI discussion guide builds a narrative arc in which the respondent gradually opens up about more difficult issues.<\/p>\n
A frequently used solution is a mixed-methods project: IDIs at the initial stage (process reconstruction, hypotheses), followed by FGIs to validate language and test concepts. The sequence can also work in reverse – a focus group interview identifies profiles that are then explored in greater depth through IDIs with selected respondents.<\/p>\n
The most common trap is treating FGI as a “cheaper version” of IDI – the argument that eight people in a group will provide more data than eight individual interviews. This is a methodological misunderstanding. Data from FGI and IDI are not interchangeable: in a group, some depth is lost, while in an individual interview, social dynamics are lost. Calculating the cost per respondent does not answer the question of which method will provide answers to the actual research question.<\/p>\n
The second error is selecting FGI for topics where group pressure distorts the result. A classic example is researching attitudes toward premium brands in a group with mixed income levels – lower-status respondents may adapt their statements to the dominant narrative, while higher-status respondents may conceal their preferences to avoid standing out. The result is seemingly consistent conclusions that are not reflected in actual behavior.<\/p>\n
The third error concerns IDIs: assuming that individual interviews automatically provide “depth.” Without an experienced moderator and a well-designed discussion guide, an IDI becomes a series of survey-like exchanges in which the respondent repeats rationalizations rather than revealing motivations. Depth in IDI is not an inherent property of the method – it is a feature of the moderator’s skill.<\/p>\n
Both techniques are also limited by the question of data saturation. In FGI, four to six groups overall or within key segments are often sufficient for recurring themes to stop adding new information. In IDI, the saturation threshold depends on the heterogeneity of the sample and the complexity of the topic – the narrower the segment and the simpler the problem, the sooner the data reaches saturation.<\/p>\n
The comparison below organizes the key operational differences that should be considered when briefing a research provider:<\/p>\n
FGI replaces IDI only when the topic is not sensitive and the objective is to understand category language or responses to a stimulus, rather than reconstruct an individual decision. In practice, full replacement is rare – more often, both methods play complementary roles within one project. If respondents represent a narrow group of experts or the topic concerns the private sphere, FGI is not a substitute for IDI.<\/p>\n
A standard focus group includes six to eight participants. Smaller groups (four to five people), known as mini-groups, are used for topics that require more space for individual contributions or when respondents are more difficult to recruit. With more than nine people, it becomes harder for the moderator to maintain group dynamics, and some participants may not have time to speak.<\/p>\n
Data saturation in IDI is achieved when subsequent interviews do not introduce new analytical categories or modify existing ones. For a homogeneous group and a narrowly defined problem, this threshold is reached sooner; for a heterogeneous sample and a complex topic, more interviews are needed. In research projects, it is recommended to monitor saturation on an ongoing basis rather than set a fixed number of interviews in advance.<\/p>\n