Response times... performance & usability testing

[textile]I was asked about response times for web applications and I remembered that Jacob Neilsen had a couple of useful articles on it... Sometimes, if you aren't given a measurable requirement, it is useful to base your assumptions about your project's requirements on some sort of generic requirement. Jakob Neilsen refers to background materials on Human Computer Interface response times and explores the web-perspective in a related article. The following explains how different wait-times alter the user's perception and experience...

**0.1 second** is about the limit for having the user feel that the system is reacting instantaneously, meaning that no special feedback is necessary except to display the result. **1.0 second** is about the limit for the user's flow of thought to stay uninterrupted, even though the user will notice the delay. Normally, no special feedback is necessary during delays of more than 0.1 but less than 1.0 second, but the user does lose the feeling of operating directly on the data. **10 seconds** is about the limit for keeping the user's attention focused on the dialogue. For longer delays, users will want to perform other tasks while waiting for the computer to finish, so they should be given feedback indicating when the computer expects to be done. Feedback during the delay is especially important if the response time is likely to be highly variable, since users will then not know what to expect. "Response Times: The Three Important Limits":http://www.useit.com/papers/responsetime.html

There is also an interesting examination of web response times in "this recently updated article - The Need for Speed":http://www.useit.com/alertbox/9703a.html