We have run discussions with as few as 6 participants but they work best if you have more. 30 is a good minimum number to aim for, though in some specific applications smaller groups make sense.
We have run sessions with 1500 participants and done testing with 2000. It is not often useful to have bigger groups than this. If you need to allow more people to participate, then run more than one parallel session.
We have had participants from 8 years old to 98. They have come from jobs as varied as cleaners and neurosurgeons. So far everybody felt able to participate in our dialogues. And they enjoy the experience!
Nowadays, texting and instant messages are everyday activities for most people. Typing means comments are more focused than talking. And those working in a second language are able to compose their sentences more easily meaning they don’t get left out.
We always reassure participants that it doesn’t matter about spelling or grammar, it’s their ideas that matter.
However, if participants have a common language other than English we can definitely run the session in that language. It is best if a session is run in just one language, though we have sometimes had two eg French and Flemish in Belgium
However open your culture – and congratulations on having one – there are things that are not easy to say in open forum. Maybe because they are critical, controversial or just feel a bit embarrassing. We know from experience that anonymity improves the truth and depth of the dialogue.
If the different groups are known to have quite points of view, then it’s best to split the segments in advance. For example. male only dialogues and female only dialogues if you are investigating the impact of gender.
An alternative is to ask 3 or 4 demographic questions on the landing page so we can segment the data during the analysis stage.
It is important to complete the feedback loop with your participants. They gave their time and ideas to you for an hour and that should be acknowledged quickly. Even if the only feedback you can give is „You gave us so much to think about! We need some time to process but will get back to you in 3 months“. They will appreciate it and be more likely to participate next time round.