The psychology of web performance

Previous research has shown that user frustration increases when page load times exceed eight to 10 seconds, without feedback. Newer evidence shows that broadband users are less tolerant of web page delays than narrowband users. A JupiterResearch survey found that 33% of broadband shoppers are unwilling to wait more than four seconds for a web page to load, whereas 43% of narrowband users will not wait more than six seconds.

Tolerable Wait Times

In a 2004 study, Fiona Nah found that the tolerable wait time (TWT) on non-working links without feedback peaked at between 5 to 8 seconds. Adding feedback, like a progress bar, pushed the TWT to an average of 38 seconds. Subsequent attempts at non-working links revealed lower TWTs, peaking at 2 to 3 seconds without feedback. Nah concluded that the TWT of web users peaks at about 2 seconds. With regard to behavioral intentions to return to a site, Dennis Galletta and others found that they level out at 4 or more seconds and attitudes flatten at 8 or more seconds.

The Effects of Slow Download Times

Even small changes in response times can have significant effects. Google found that moving from a 10-result page loading in 0.4 seconds to a 30-result page loading in 0.9 seconds decreased traffic and ad revenues by 20%. When the home page of Google Maps was reduced from 100KB to 70-80KB, traffic went up 10% in the first week, and an additional 25% in the following three weeks . Tests at Amazon revealed similar results: every 100 ms increase in load time of Amazon.com decreased sales by 1%.
Experiments at Microsoft on Live Search showed that when search results pages were slowed by 1 second:
- Queries per user declined by 1.0%, and Ad clicks per user declined by 1.5%
After slowing the search results page by 2 seconds:
- Queries per user declined by 2.5%, and Ad clicks per user declined by 4.4%

The Effects of Slow Response Times on User Psychology

Slow web pages lower perceived credibility and quality. Keep your page load times below tolerable attention thresholds, and users will experience less frustration , lower blood pressure, deeper flow states, higher conversion rates, and lower bailout rates. Faster websites are actually perceived to be more interesting and attractive.

Conclusion

The old 8 to 10 second rule has diverged into the haves and have nots. Broadband users expect faster response times, while narrowband users have been left behind. As broadband becomes more widespread the size of the average web page has increased to over 300KB and the average number of objects has increased to over 50 per page. Users experience psychological and physiological effects when interacting with web pages, experiencing frustration when not completing tasks and engagement at faster web sites. Narrowband users are suffering the most from the speed tax of objects that now dominates most web page delays. Increasing the speed of your site will improve your conversion rates, reduce shopping cart bailout rates, and make your site more appealing to users.

Source: Web Site Optimization