Software Speed and User Experience

Mark Bernstein publishes so much insightful commentary that it is surprising when you discover something crying out for further examination. The Economics of Speed is one such case.

When Bernstein asks, “Is speed worthwhile?” he rather off-handedly—and rashly—dismisses “user experience” as the driver for increased speed.

His argument seems to be that, while a few seconds for a single user is irrelevant, those few seconds aggregated across his user base is significant. But this rationale is plainly wrong: those seconds can’t be aggregated in any meaningful way; summing my time, and Mark Anderson’s time, and Jean Goodwin’s time, and every other Tinderbox user’s time spent waiting for the software is purely a mathematical construct. I’m certainly not willing to pay for the seconds themselves—I “waste” far more time than a few seconds in chit-chat around the office…

The real reason

The real reason for improving application responsiveness is to prevent the application from interrupting the user's psychological experience of flow. While a couple of seconds does not seem economically valuable, being jolted out of flow damages productivity far beyond the duration of the interruption.

Usability Engineers have known for three decades the critical human factors thresholds for optimal user experience. Interestingly, these thresholds provide guidance as to how much engineering should be invested into application responsiveness. Keeping an application within these responsiveness thresholds increases the possibility of the user maintaining flow.

So while Bernstein asserts, “User experience is not what matters,” I argue that it is the critical rationale for investing in application responsiveness.

Aside: I hope to see some of you at UX Australia 2009 next week.