How many people should I interview for creating a valid persona

Question

How many people should you ideally (when time and money isn't a problem) interview before you could see clear patterns to create a valid persona? I've seen answers between 5 to 30. I'm working on a web site . The client's marketing department have already divided their market into 4 need-based segments so I feel confident to start building personas based on these groups to understand why and how they would use the web site.

Answer 1

I'd say it depends on the complexity of the project. 'Web site' can be easy, but addressing 4 segments doesn't sound too easy. On the user hand it sounds pretty good that the clients' marketing team seems to have a clear picture.

For the number of interviews:

Kim Goodwin has written a useful blog post about it and suggests 12 interviews, but up to x-times 12 interviews, depending on the complexity:

A dozen hour-long interviews are usually sufficient for defining a simple consumer product, though it can take several dozen for a complex enterprise application.

A bit in contrast, a UX Magazine article states that patterns in the data start to emerge after approx. 30 interviews.

My personal opinion is that the most important thing is to talk to potential users/customers at all (ideally equipped with some wireframes), regardless if for the purpose of creating personas or not. It's a good way to get a wider picture and at least some pre-launch validation of assumptions. I am sure you know this but I am not sure if your client does. I would talk to the client and show that there is no evidence or clear direction amongst experts and then recommend whatever you think is appropriate and get their feedback.