So, semi-structured interviews – well, any interview, semi-structured or not, gets at people's perceptions, their values, their experiences as they see it, their explanations about why they do the things that they do, why they hold the attitudes that they do. And so, they're really good at getting at the *why* of what people do,
but not the *what* of what people do. That's much better addressed with *observations* or *combined methods* such as contextual inquiry where you both observe people working and also interview them, perhaps in an interleaved way about why they're doing the things that they're doing or getting them to explain more about how things work and what they're trying to achieve.
So, what are they *not* good for? Well, they're not good for the kinds of questions where people have difficulty recalling or where people might have some strong motivation for saying something that perhaps isn't accurate. I think of those two concerns, the first is probably the bigger in HCI
– that... where things are unremarkable, people are often *not aware* of what they do; they have a lot of *tacit knowledge*. If you ask somebody how long something took, what you'll get is their *subjective impression* of that, which probably bears very little relation to the actual time something took, for example. I certainly remember doing a set of interviews some years ago
where we were asking people about how they performed a task. And they told us that it was like a three- or four-step task. And then, when we got them to show us how they did it, it actually had about 20, 25 steps to it. And the rest of the steps they just completely took for granted; you know – they were: 'Of course we do that! Of course we—' – you know – 'Of course that's the way it works! Of course we have to turn it on!' And they just took that so much for granted that *it would never have come out in an interview*.
I mean, I literally can't imagine the interview that would really have got that full task sequence. And there are lots of things that people do or things that they assume that the interviewer knows about, that they just won't say and won't express at all. So, interviews are not good for those things; you really need to *observe* people to get that kind of data. So, it's good to be aware of what interviews are good for and also what they're less well-suited for. That's another good example of a kind of question that people are really bad at answering,
not because they're intentionally deceiving usually, but because we're *not* very good at *anticipating what we might do in the future*, or indeed our *attitudes to future products*, unless you can give somebody a very faithful kind of mock-up
and help them to really imagine the scenario in which they might use it. And then you might get slightly more reliable information. But that's not information I would ever really rely on, which is why *anticipating future product design is such a challenge* and interviewing isn't the best way of getting that information.