While determining a sample size is easy for an online survey (for example, brand awareness research), the same cannot be said for the number of interviews in qualitative research. The principle of saturation is often put forward as the ultimate argument for determining the sample size. But it is challenging to implement. To help you, we have launched the first version of an online tool to calculate the minimum number of interviews to be conducted.
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Individual interviews are a “qualitative” method, just like focus groups. The difference between the two approaches lies in the objectives pursued. Qualitative interviews aim to “explore,” whereas focus groups seek to “confirm” working hypotheses.
Qualitative methods are used in many fields to “clear” a subject and explore the different themes related to it.
Our online calculator is limited to a particular perspective: understanding customer needs within the framework of market research.
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Why conduct interviews as part of market research?
Market research aims at assessing the business potential of an idea. Determining the right idea requires a good understanding of the needs of future customers. To explore these needs in-depth, nothing is better than qualitative interviews. But the problem is that it is complicated, in principle, to determine the number of interviews to conduct.
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Factors that determine the number of interviews to conduct for your market research.
The number of interviews you need to conduct depends on the subject you are interested in and the stage you are at in the market research.
Finding an idea vs. confirming an idea
Finding a business idea that meets a need is not the same as confirming the relevance of an idea with your target audience. In the first case, you need to interview more people to understand their current and future needs. In the second case, it will be “enough” to present your idea to a sample of people to collect opinions and improve your chances of success.
Face-to-face or remote interview?
Qualitative interviews conducted face-to-face make it possible to mobilize the respondent and to have his full attention. With the Covid crisis, qualitative market research had to be conducted remotely. Distractions and temptations are more numerous when one is behind his screen. Moreover, body language is less easily perceived. Qualitative interviews carried out at a distance are therefore less effective, and for this reason, more should be carried out.
Different uses depending on the target?
In some contexts, a product can meet different needs. For example, Europeans will use a Smartphone to make phone calls, but for 97% of Africans, it is the only way to connect to the Internet. The constitution of a qualitative sample must be oriented by the need you want to explore. If different consumer segments have radically different needs, you will need to multiply the instances to understand the dynamics of each group.
Disruptive or incremental innovation?
Improving an existing product does not present the same challenges as creating an entirely new product/service. In the first case, it is possible to assume that the respondent knows the product’s use and asks him/her about the improvement. In the second case, since the pre-existing usage does not exist, the respondent must project himself into a completely new situation. This effort is not within reach of everyone and will necessarily require more interviews.
Qualitative interviews are an indispensable exploratory approach to any market research. Determining the number of interviews in advance is not easy. Our sample size calculator will help you do so, depending on the objective of the market research.
To go deeper into the subject
We used the following scientific sources in the development of our calculator. We advise you to read them if you want to know more about the subject.
Dworkin, S. L. (2012). Sample size policy for qualitative studies using in-depth interviews.
Marshall, B., Cardon, P., Poddar, A., & Fontenot, R. (2013). Does sample size matter in qualitative research? A review of qualitative interviews in IS research. Journal of computer information systems, 54(1), 11-22.
Mason, M. (2010, August). Sample size and saturation in PhD studies using qualitative interviews. In Forum qualitative Sozialforschung/Forum: qualitative social research (Vol. 11, No. 3).
Morse, J. M. (1994). Designing funded qualitative research.
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