usability versus usage -- an iPhone example
Today, I noticed an article in Information Week titled Businesspeople Face Steep Learning Curve with iPhone, which discusses a usability test conducted against the iPhone from a company called User Centric, Inc. This is excellent timing. I've had a post banging around the inside of my head about the difference between usability and usage, and here's a great example of the difference.
Jakob Nielsen says that usability is defined by the following five quality components:
- learnability: how easy it is to do a task the first time you encounter it
- efficiency: how quickly you can perform the task
- errors: how many errors you make, the severity of the errors, and how you recover
- memorability: how well you remember the task and can apply that knowledge in the future
- satisfaction: how happy you are with your experience
These five quality components are measured in most standard usability tests, with a heavy focus on the first three components. You can get a snapshot of the latter two, but this snapshot doesn't necessarily measure them in a meaningful way. Remembering how to do a task ten minutes after I've done it the first time is very different than having to remember how to do a task ten weeks after I've done it the first time. Likewise, my level of satisfaction changes over time. I could have been absolutely over the moon about a feature when I first encountered it, but somehow grew annoyed by it or found that it wasn't as useful a few weeks later.
That is the difference between usability and usage. Usability is measured up-front, and is often a first impression. Usage, on the other hand, is measured over time. Both have their place. If you can't use a feature right out-of-the-box, it's unlikely that you're ever going to get over that initial hurdle.
This iPhone study is a great example of the difference between the two. It specifically compares the usability of an iPhone with the usage of existing phones (both standard 12-button cell phones and smartphones with a QWERTY keyboard). They recruited for users who text frequently on their existing phone, and asked them to do the same tasks on an iPhone and on their own phone. It is entirely unsurprising that users couldn't text on the iPhone as well as they could on their own phones. After all, they know their own phone quite well, and they're frequent texters. Using something entirely new, which has a completely different model of use, will obviously present them with problems. They had expectations based on their current usage of their existing devices, and those expectations don't match up with the iPhone.
These types of studies are pretty common in usability circles. Many competitive usability studies are built around this model: take users of an existing piece of software, and give them tasks against both that software and a competing piece of software that they've never used before. It's a great way to collect feedback about what people like and don't like about both pieces of software. It also helps you to identify places where you might need to overcome the initial usability issues inherent in transferring from one technology to another, and where you'll have to do something to either make the learning curve flatter or to make the learning curve seem like less of an obstacle.
The important thing to remember about this kind of comparison of usage and usability is that it's only a first impression of whatever you're doing the usability test of. In many cases, it is the first stepping stone to doing more work and developing a greater understanding of the differences between two products. User Centric, Inc, says in their iPhone study FAQ that they plan to do further work about iPhone usage. To quote from the FAQ, '[w]e may find that iPhone users with experience may be more efficient, but we need to do the study first'.
I'll be interested to see future studies of iPhone use. I'd love to know if an experienced iPhone user is still slower at texting than a similarly experienced smartphone user, not to mention how satisfied each of them are with their experience. This is the first step towards understanding the difference between iPhone usability and iPhone usage, but it is by no means the last one.
