As you would expect the answer to this question is that it depends.
We often quote for projects of 6 groups (we have 5 respondents in each) because in our experience over nearly 20 years with our particular methodology we have found that for a standard research project this will give us a stable result.
To explain this I need to expand upon what I mean by a “standard project” and what I mean by a “stable response”.
A Standard Project
This, for us, is a project of six groups. This will have a single or maybe two socio-economic/demographic target groups, one or two locations and up to 6 SKUs (client or competitive products, concepts etc.) to study.
Reducing the number of products, socio-economic or demographic groups or even locations is unlikely to reduce the need for 6 groups as we start to get just too few respondents to get a stable response. Increasing the number of products or complicating the socio-economics/demographics or locations will increase the number of groups required to ensure a stable response and to ensure that we spot any differences between the different target groups.
Sometimes as well, the project is just a bit more complicated or difficult and we will build in a couple of extra groups to ensure we get a really solid response and can be completely confident in our recommendations.
What do I mean by a “Stable Response”?
As we cross question each individual respondent we get very deep insights into their personal emotional drivers and their emotional responses to the products/concepts that we are studying. This is fascinating to us as psychologists, but of limited use to our clients.
However, as we repeat this with an increasing number of respondents, we start to find the common emotional drivers and emotional responses. We then get to a stage when we can reliably predict how respondents will respond and what they will say. This is what we term a “Stable Response”.
Experience over the last 20 years has shown us the number of respondents that is required per SKU for us to get to this Stable Response and foe a standard project that will require 6 groups.
So, how many Groups will my Project Require?
One we understand your brief we will be able to work out how many groups will be required to reach a stable response. We normally start at six groups and will add more when required to ensure we reach a stable response and we can be confident in our findings and recommendations.
Adding groups does of course lengthen the project and increase costs, so we will always keep it as small as we believe possible. Also, the exciting part of any project is in reaching that stable response, in getting to the point where we understand what is happening and why and subsequently how we can help the client move forward from this point. Once we get to a stable response the work becomes quite repetitive and boring. We know what the respondents are going to say. We like to keep our work interesting, so we have no interest in adding extra groups unnecessarily.