Responsiveness

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The responsiveness of an interactive system describes how quickly it responds to user input (i.e. the rate of communication with the system). It is one of the criteria under the principle of robustness (from a usability principle). The other three are observability, recoverability, and task conformance.

Responsiveness vs Performance

It is quite obvious that systems with a fast hardware, and a software optimized on speed, will generally provide a better responsiveness.

However, it can be much more important that a system does actually spend the available resources in the best way possible. For instance, it makes sense to let the mouse driver run at a very high priority, to provide fluid mouse interactions. Long-term operations, such as copying, downloading or transforming big files, can quite well run in the background, using only spare processor time.

Software which lacks a decent process management, can have poor responsiveness even on a fast machine. On the other hand, even slow hardware can run responsive software.

Influential Factors and Testing

There are many factors that can influence the responsiveness of an interaction system, such as poor design, improper input from users, problems with the operation system or the network. It is generally a good practice to have the designer(s) of the system play the role of the user and run diagnostics to determine if it causes any unreasonably long delays.This will allow them to affect any changes that need to be made before the system is introduced to the users worldwide,thus avoiding such problems earlier on in the systems life-cycle.

Delays

Long delays can be a major cause of user frustration, or can lead the user to believe the system is not functioning, or that a command or input gesture has been ignored. Responsiveness is therefore considered an essential usability issue for human-computer-interaction (HCI). The rationale behind the responsiveness principle is that the system should deliver results of an operation to users in a timely and organized manner.

The frustration threshold can be quite different, depending on the situation. The three "magic numbers" are 0.1s, 1s, and 10s.

See also

• http://www.useit.com/papers/responsetime.html
• http://performance.netbeans.org/responsiveness/whatisresponsiveness.html
• http://developer.gnome.org/projects/gup/hig/2.0/diff-from-1.0/feedback-response-times.html

Solutions to Improve Responsiveness

Although numerous other options may exist,the most frequently used and recommended answers to responsiveness issues are:

• Optimizing the process that delivers the output by eliminating wasteful,unproductive output from the algorithm or method by which the result is produced.
• A decent process management system, giving highest priority to operations that would otherwise interrupt the user's work flow, such as typing, onscreen buttons, or moving the mouse pointer. Usually there is enough "idle time" in between, for the other operations.
• Using idle time to prepare for the operations a user might do next.
• Let the user do something productive while the system is busy - for instance, writing information in a form, reading a manual, etc. For instance, in a tabbed browser, the user can read one page while loading another.
• Deliver intermediate results, before the operation is finished. For instance, a web page can already be operated before all images are loaded,which will take up the idle time which would otherwise be spent needlessly.
• If some waiting is inevitable, a progress indicator can significantly reduce frustration. For short delays, an animated icon might be sufficient. Longer delays are better covered with a progress bar, or, if possible, the system should provide an approximation of the time that an operation is going to take before starting it.
• Provide a control to stop the process and try something else.

See

• http://www.baychi.org/calendar/20031111/

See also

Responsivity, a related concept in electrical engineering.

Reactivity, an unrelated concept in chemistry.

External links

• [1] Chapter 9. Constructing A Responsive User Interface. by David Sweet

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