CHAPTER 4 Culture of Performance
within your industry perform by referring to the Keynote performance
indices^11 which break down analysis by industry type.Now that you know how your site performs, as well as how your com-
petitors fare, you can make an informed decision about what budget to
settle on using Weber’s law and the 20% rule.The 20% Rule
German physician E.H. Weber observed that the noticeable difference be-
tween two properties varies in proportion to the size of the properties. For
example, it’s easier to tell the difference between one hour and two hours
than it is to tell the difference between one minute and two minutes.
Applying this to computer interaction, Steven C. Seow came up with
the 20% rule in his book, Designing and Engineering Time: The Psychology of
Time Perception^12. Put simply, to create a noticeable improvement in perfor-
mance as perceived by your visitors, you need to improve performance by
at least 20%.
If you apply this rule to the metrics you’ve found for your current site,
you can come up with the bare minimum of improvement. If your page
loads in 10 seconds, making it load in 8 seconds or less would provide a
noticeable improvement; 9 seconds, much less so.
Applying the 20% rule to the metrics from your competitors can help
you determine at what point you would provide a large enough improve-
ment in performance to truly distinguish your site as faster.
For example, if your competitor’s site loads in 5 seconds, you want to
get your site under 4 seconds at the very least.
The ultimate goal is to make the experience as fast as possible for your
visitors, but the 20% rule can provide a good starting point.11 http://www.keynote.com/keynote_competitive_research/index.html
12 http://www.engineeringtime.com