Latency
Latency is another term for delay. The term is typically used in an engineering sense, where latency refers to the delay between the moment something is initiated and the moment its first effect begins.
In usability terms, latencies refer to the delay between the moment the user performs some action and the moment they receive feedback on the status of that action. Large latencies are generally considered bad, and something to be eliminated.
The following are good heuristics when considering latency in the context of the user experience:
- Reduce the user's experience of latency
- Acknowledge all button clicks by visual or aural feedback within 50 milliseconds
- Display an hourglass (or other similar device) for any action that will take from 1/2 to 2 seconds
- Animate the hourglass (or other similar device) so they know the system hasn't died
- Display a message indicating the potential length of the wait for any action that will take longer than 2 seconds
- Communicate the actual length through an animated progress indicator
- Offer engaging text messages to users informed and entertained while they are waiting for long processes, such as server saves, to be completed
- Make the client system beep and give a large visual indication upon return from lengthy (>10 seconds) processes, so that users know when to return to using the system
- Trap multiple clicks of the same button or object. Because the Internet is slow, people tend to press the same button repeatedly, causing things to be even slower
- Make it (everything) faster - eliminate any element of the application that is not helping. Be ruthless
- Wherever possible, use multi-threading to push latency into the background - long latencies can often be hidden from users through multi-tasking techniques, letting them continue with their work while transmission and computation take place in the background
Learnability
Learnability is a measure of the degree to which an interface - for a product, system or service - can be learned quickly and effectively: time is the usual measure here. In an ideal world, products or systems would have no learning curve of any description: users would walk up to them for the very first time and achieve instant mastery. In practice, all applications and services, no matter how simple, will display a learning curve.
- Limit the trade-offs - usability and learnability are not mutually exclusive. First, decide which is the most important; then attack both with vigour. "Ease of learning" automatically coming at the expense of "ease of use" is a myth.
Lickert scale
Lickert scales are used to measure personal values such as attitudes, preferences and other subjective qualities. An example is shown below:
I find this Jargon Buster easy to use |
Strongly disagree |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
Strongly agree |
Lickert scales - and other attitudinal scales - help to get at the emotional and affective responses that people have to products, systems and services.
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