Having written about both Discoverability and Findability, I feel obligated to address Learnability as the next vocabulary term.
Learnability is not a term specific to Interaction Design. Dictionaries will provide definitions such as “the condition of being learnable” and “the ease with which something can be learned.” That’s clear enough, but the term does have more specific meaning when used in the context of Interaction Design. Here’s a definition from Usability First’s glossary:
a measure of the degree to which a user interface can be learned quickly and effectively. Learning time is the typical measure. User interfaces are typically easier to learn when they are designed to be easy to use based on core psychological properties, and when they are familiar. Familiarity may come from the fact that it follows standards or that the design follows a metaphor from people’s real world experience.
Tristan Louis breaks learnability down into five components:
While I would consider learnability to be a component of usability, it is often discussed in contrast to usability. For example, Jeff Atwood’s article, Usability vs. Learnability, quotes a passage from Joel Spolsky’s book, User Interface Design for Programmers:
It takes several weeks to learn how to drive a car. For the first few hours behind the wheel, the average teenager will swerve around like crazy. They will pitch, weave, lurch, and sway. If the car has a stick shift they will stall the engine in the middle of busy intersections in a truly terrifying fashion.
If you did a usability test of cars, you would be forced to conclude that they are simply unusable.
This is a crucial distinction. When you sit somebody down in a typical usability test, you’re really testing how learnable your interface is, not how usable it is. Learnability is important, but it’s not everything. Learnable user interfaces may be extremely cumbersome to experienced users. If you make people walk through a fifteen-step wizard to print, people will be pleased the first time, less pleased the second time, and downright ornery by the fifth time they go through your rigamarole.
Sometimes all you care about is learnability: for example, if you expect to have only occasional users. An information kiosk at a tourist attraction is a good example; almost everybody who uses your interface will use it exactly once, so learnability is much more important than usability. But if you’re creating a word processor for professional writers, well, now usability is more important.
Now, I get what Joel is saying here, but I don’t believe he has his terminology quite right. I think he is using learnability where he should be using intuitiveness, and that may just have to be my next Design Vocabulary entry. If you sit somebody down in front of a UI for the first time, you will be testing how intuitive it is to use. If you want to test for learnability, I suggest that the test must be repeated over a number of sessions. Michael Wilson corroborates this claim in his informative article on the subject, When is Learnability More Important than Usability? That said, intuitiveness could really be considered as the ultimate achievement of learnability: the shortest possible learning time.
Michael also lists the factors that will most likely result in a user spending the time required to learn a given user interface:
All of these cited articles are useful in understanding learnability, but Justin Mifsud has the most complete perspective. In The Difference (And Relationship) Between Usability And Learnability, he explains that many writers “tend to over-emphasize on highlighting the distinction, yet they fail to discuss the relationship that exists between usability and learnability.” He goes on to site definitions put forth by IEEE and ISO, which classify learnability as a sub-characteristic of usability, on par with understandability, operability, and attractiveness, as well as Jakob Nielsen and Ben Schneiderman’s classification, which lists learnability as one of five parameters that define usability, its siblings being efficiency, memorability, errors, and satisfaction.