Common Sense Trumps Statistics

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COMMON SENSE TRUMPS STATISTICS
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Who cares about performance? Hint its your
customers! Speeding up your site by several
seconds, or even by just a few hundred
milliseconds, will make your customers happy.
Well, at least theyll be less irritated. Thats
pure logic. I am not citing statistics, I am
using common sense. For example, a 50 decrease
in file size cutting bloat in half has a
greater impact on someone on 2G on mobile than on
a T1 line. Common sense dictates the impact is
greater on a 5Mb site than a 5Kb one, no matter
the network speed, as performance gains achieved
by halving a 5Kb download may not even have a
noticeable effect. Similarly, improving a 12s
page load to 11s doesn't have the same impact as
improving a site from 3s down to 2s. The impact
of a one-second improvement depends on the
original experience. This is obvious. It's common
sense. Conclusions based on common sense are
often accurate, but arent considered factual
like conclusions based on statistics. Statistics
are often used to demonstrate something as fact,
but a statistic is really only a fact about a
piece of data. Mark Twain is credited with saying
Facts are stubborn things, but statistics are
pliable. We discuss web performance statistics
as if the web were a monolith, as if all web
applications were uniform, as if performance
improvement effects are linear. They may not be
represented by a simple exponential equation, but
performance isnt a simple science, and metric
interpretation shouldnt be assumed to be linear,
or even accurate. The statistic web speeders
often quote, a one-second delay in web page
responsiveness leads to a 7 decrease in
conversions, an 11 drop in pageviews, and a 16
decrease in customer satisfaction," is pretty
inaccurate today. This quote comes from a 2008
study a study that came out a few months after
the iPhone SDK was released and Android Market
came into being, and before either proliferated.
When that study was conducted, the iPad and
Android tablet were a few years off. As web
speeders, we can't quote a performance study that
basically predates mobile. Yet, that's what we're
doing.
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While the customer satisfaction statistics might
not be exactly true, the conclusions are not. The
longer the site takes to load, the less happy
your customers will be, the more users will
abandon your site, the lower your conversion
rates will be, and the less money you'll make.
It's not even that your customers will be unhappy
it's that they may not be your customers
anymore. That's common sense, no matter what the
actual percentages are. Definitely give yourself
a performance budget and test your site. Test
your application throughout the development
process. Optimize and right-size your images,
setting dimensions. Reduce DNS lookups. Reduce
bloat, minimizing request size, GZipping all
requests. Make fewer HTTP requests or serve
content over HTTP/2, caching what you can.
Basically, follow as many performance
recommendations as you can. Improve the
performance of all of your content, not just your
home page. Focus your energies on the critical
path of your site. Its obviously less important
to optimize some pages, say the libraries we
use page linked to from an about us page
linked to from a political candidates website.
But do realize users often enter your site thru
a side door for example, a product page, with
the shopping cart experience being a necessity
for all sales for an online store. In the case of
eCommerce, optimizing your homepage might create
the most savings," but will do little to improve
user experience for your actual potential
customers. And never forget improving the
download speed is not enough improving your
site's load time by one second won't improve
customer satisfaction if, once loaded, theyre
met with an unresponsive UI. Or maybe it
will. Let me go back to 2008 to test that out.
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