One of the bigger problems that designers and testers have in the way of usability is in working out a really good way to not only accurately measure it, but to implement standards for good and bad when it comes to the metric you get. In the past, many people have worked out their on guidelines and measurement systems, and this has resulted in, when case studies and published materials are released, a lot of confusion, and it makes usability difficult to actually measure. However, with the advent of the system usability scale (SUS), this isn’t nearly the problem it used to be.
The system usability scale is a series of ten questions with degree- based answers, one for strongly disagree, five for strongly agree. After the questions are answered, the numbers are tallied (and multiplied by 2.5) for an overall score. Now, fortunately, there is more or less a consensus on what a good score, when using the SUS, might be. A 68 is considered very good, and some variance in either direction is to be expected. So, the SUS is a very good, easy to use and pretty unanimously accepted scale to measure usability. That makes this all much less of a hassle. Well, this wasn’t that time consuming to explain, so let’s take some of the extra time we have, to talk about the questions commonly asked in the SUS.
1 – I could see myself using this very frequuently. This is a good measure of if the system becomes frustrating when used regularly.
2 – This system was far too complex. This is a good look at if the design should be simplified. Don’t feel bad if this one tends to jack your score a little.
3 – This seemed quite easy to use, to me. They may not find it complex, but that doesn’t mean they found it pleasantly easy to use, so this one covers that base.
4 – I would probably need a tech person to help me figure this thing out. This shows if the system has a steep learning curve, or is intimidating at first appraisal.
5 – It seemed to me that the various functions of this system tied together very, very well. This reads if everything integrates and is consistent.
6 – I thought too many things were inconsistent with this design. This follows the previous, because just because it seems well integrated does not mean other inconsistencies aren’t there.
7 – I think most people could probably learn this system without any problems or confusion. This is the equivalent of “would you recommend this” on with a technical perspective.
8 – I found this system very awkward to use, enough to make the whole thing tiring. Another follow up, just because it’s easy to learn doesn’t mean it’s not awkward.
9 – I found this very comfortable to work with, and I was confident and unintimidated. This is another look into how immediately adoptable and comfortable the system is.
10 – It took me a lot of learning and figuring out to get anything basic done with this design. This is a good look at if the initial state needs to be a bit more user centric and less technical.
So, there you have the system usability scale, how it works, how to implement it, and what the questions are. It makes perfect sense to use a scale like this to measure usability, and many such scales have been tried. This is, however, the first one mostly everyone seems to have agreed on!