This post by Christopher Fahey of graphpaper.com got me thinking about the longitudinal nature of usability issues, and what it means for user experience research & design.

Now: the teething problem
This is a usability issue that you experience at first, but eases off as you get used to the product. For example, the first time you used an ipod you probably had at least 30 mins of familiarization and teething problems (“hey, this isn’t like my minidisc player, but it is kind of cool…”).

Later: the ill fitting shoe
This is a usability issue that you don’t notice at first, but it becomes increasingly bothersome as time wears on. For example, some voicemail systems that plays you the same long introductory message every time – educational at first, but after a while you start to notice every second it is stealing from your life.

So, what does this means for evaluation?

User tests often evaluate the first 60-90 minutes of use. This is a defining period but how much time the average person will use the product in total? If they are clocking up many hours of use every week, then the first hour of use is, in a sense, just a edge case.

To evaluate this product’s user experience, you’d have to employ longitudinal techniques – diary studies, repeat testing, telescoping, betas, and of course maintain an open dialogue with your customers.

If you don’t take a longitudinal view, then you are at risk of angling your product too specifically at beginners, and in doing so alienate the experienced users – or vice versa. Research methods are like a narrow beamed flashlight in a dark cave. To get a good view of things you have to expend a fair amount of effort looking at things from different angles.

And what does it mean for innovation?
Sometimes, when you try to avoid teething problems, you conform to the status quo, and you don’t help users in the long run. Imagine if the iPod ended up looking like the Creative Rio Mp3 player, because people in the user test sessions couldn’t quite get their heads around the concept of click-wheel navigation.

But sometimes arrogance can get the better of you. So some teething problems go away – how do you know if your design will do this? And, even if it does, can you justify the pain?