Attention Spans and Response Times: How Fast is Fast Enough?

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Your brilliant web application and marketing efforts have won you visitors and recognition. But there’s a ticking time bomb built into every interaction on your site. In about 1 second your potential customer is going to start thinking about doing something else.

The Experts Say…

Usability expert Jakob Nielsen calls it a fight against “the inevitable decay of information stored in short-term memory” [1]. How quickly your web application responds will have an impact on your engagement and the attitude towards your site.

In 2006, Google famously experimented with displaying 30 results per page instead of 10. But the extra results forced loading times up to 0.9 seconds from 0.4 seconds.  The result was a 20% drop in ad revenue [2].

Google being Google probably didn’t lose too many customers in the long run. But for a relatively unknown startup, it could be a large price to pay.

A 2006 study from Akamai states that “fifty-five percent of online shoppers who spend more than $1,500 online per year insist on pages loading quickly” [3].

How fast is fast enough?

It turns out web pages are no different from any other interaction. Our levels of patience over time follow a pattern that’s easy to remember [1]:

0.1 seconds gives the feeling of instantaneous response — that is, the outcome feels like it was caused by the user, not the computer. This level of responsiveness is essential to support the feeling of direct manipulation

1 second keeps the user’s flow of thought seamless. Users can sense a delay, and thus know the computer is generating the outcome, but they still feel in control of the overall experience and that they’re moving freely rather than waiting on the computer. This degree of responsiveness is needed for good navigation.

10 seconds keeps the user’s attention. From 1–10 seconds, users definitely feel at the mercy of the computer and wish it was faster, but they can handle it. After 10 seconds, they start thinking about other things, making it harder to get their brains back on track once the computer finally does respond.

Three Factors

Now that we know keeping response times under a second is crucial to a happy user experience, let’s look at the factors that make up a response on the web:

(Server response + Browser render) + Latency 

The parts you have control over are server response and browser render time. Tools like NewRelic help you keep tabs on those times and should notify you when they become intolerable.

Response time visualization

Latency, however, is mostly out of your control. It’s the time it takes for information to travel between a device and your server. Since the rise of broadband internet connections, latency time has generally stabilized to well under 0.1 seconds.

Mobile Latency

But the new surge in mobile devices has reintroduced latency as a problem. Average latency on mobile devices ranges from 0.1 - 1 second. Latency on Sprint’s 4G network averages 0.15 seconds. On their 3G network requests average 0.4 seconds [4]. So now just to satisfy your mobile customers, you need your server response time under 0.6 - 0.85 seconds just to keep the average mobile user engaged.

It’s up to you your and your engineering team to stay aware of those response time numbers and keep them down to a tolerable level.

So while your marketing efforts will land users on your site, make sure you devote some effort on response times to prevent them from wandering off and keep them coming back for more.

- David Wright

[1] http://www.useit.com/papers/responsetime.html 
[2] http://glinden.blogspot.ca/2006/11/marissa-mayer-at-web-20.html
[3] http://www.akamai.com/4seconds
[4] http://www.igvita.com/2012/07/19/latency-the-new-web-performance-bottleneck/