User interview

There's no magic answer to this question. The only guarantee is that a single interview is better than none at all. In qualitative approaches, we talk about saturation, the point from which you no longer learn anything new. When the profiles are homogeneous (e.g. a group of users of one service), you get very rich results even with fewer than ten users involved. It all depends on your context!

The real risk in an interview, whatever the type, is social desirability. In a test context, participants tend to say what they think is expected of them, or to rationalise behaviours they hadn't really deliberated. It's to avoid this bias that we refrain from asking someone what they think. We favour recalling a recent situation, along the lines of « tell me about the last time you tried to... ». This gives access to a concrete lived experience, not an opinion reconstructed after the fact.

Depending on the interview format and the type of data recorded during a user interview, the analysis can vary. Very generally, you start by gathering the participants' answers across the different themes discussed. From this raw material, you can then begin to look for whether themes recur and see how the participants interviewed break down according to their answers. When the interviews are transcribed, you can also carry out a discourse analysis. For each UX project the goals vary, so the principle of the analysis is to confront the material collected with the hypotheses and/or the points that interest us most for a study.

A successful interview relies on good preparation. Both on creating the interview outline, with the choice of themes, and on the format you offer for answering. You can for instance draw on sharing positive or negative anecdotes to get people talking about a lived experience. You can also imagine offering answers in the form of a top 3 of situations encountered, or asking what they would do if they had a magic wand. The aim is to lead the user to share as much detail as possible without feeling they are being interrogated. It's the art of questioning.

The follow-up question is very important for a one-to-one interview. Once you've defined the themes to discuss with a user, you list specific follow-up questions. These questions are designed to help steer the discussion towards sub-themes smoothly during the exchange. During the interview, they let you carry on after an answer, ask for more detail, ask why a given answer, and so on.