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What is the optimum length of a focus group?

Photo of Hourglass. Best length for focus groups?

I’ve been at this lark since the last century, and it seems to me that the length of time we expect participants to commit to a focus group, and to make a useful contribution, has gradually been creeping up over the years.

How long is a piece of string?

When I started out in research, a group discussion (as we referred to them before we bowed to the inevitable and accepted the US term focus groups) usually lasted 1½ hours. Nowadays I would only ever recommend 1½  hours if I have a client with a tight budget and I am trying to keep respondent incentive costs as low as possible without deterring potential participants.

Two hours seems to have become the standard (or even the minimum), and to be honest, by the time the stragglers have arrived (those who couldn’t find the building, or got stuck in rush hour traffic) several minutes have probably been lost, so we’re already down to about 1 hr 50 if we’re lucky.

Many of my clients are based in mainland Europe. It is unusual for them to consider groups of a shorter duration than 2.5 hours, and they often go for as long as 3 hours. This can work if there is plenty of stimulus to show, and interesting things for respondents to do. But towards the end of a 3 hour group that may have started at 7pm, the energy level in the room can start to drop, and responses simply become less useful – so it is important to include plenty of changes of pace and activity.

How should you calculate the time you need?

When deciding how long a group should run, it is important to take a number of issues into consideration

Sample – Assuming respondents are adults, without disabilities, up to 3 hours is probably feasible (though not always advisable, for the reasons mentioned above) 

Number of respondents – Groups are generally amongst 6-8 respondents, so 1½ to 2 hours gives everyone an opportunity to share their point of view. ‘Mini-groups’ eg 4-6 respondents can be completed in a slightly shorter time without limiting individuals’ opportunity to have their say

Subject matter – It is possible to run a group which is both lengthy and lively. Young men, can be so engrossed in talking about computer games that they are still going strong after 3 hours. But there is a limit to the length of time that most of us can sustain our concentration in a discussion of credit card statement layouts, or supermarket price labelling – so it is important to keep it interesting. Projective techniques can help with this, and are a topic for another blog which is coming soon. And if you do have a longer group – avoid leaving the most important part of the discussion to the end if at all possible

Research objectives – By this I don’t simply mean the amount of ‘stuff’ to be covered (though this certainly influences the amount of time needed), I also mean the type of information needed. The more exploratory the research, the more time is needed to uncover relevant and new insights sensitively and with the richness that supports clients to make the right decisions

Stimulus – A key element is the ‘stimulus’ to which participants are exposed. This can range from rough concepts, through draft marketing communications, to finished products, and can keep a group interested and involved. However, people need to be given time to evaluate what they are shown, and this needs to be allowed for in the group.

Budget – There is a sudden hike in cost when group length goes from 2 hours to 2½ hours. The simple reason for this is that it is not possible to run two longer groups in the same evening, so one of them has to be held during the day. This increases venue costs substantially, and also requires a higher respondent incentive.

The real worth of qualitative research lies in its depth of understanding, and richness of insight. And in the end, this can perhaps be better achieved not by increasing the length of the group, but by limiting or prioritising the amount covered. That way we ensure that we provide a depth of understanding that will support our clients in their business decisions.