Google Website Optimizer v 1.0 The Techie Guide - Manual (Page 7)

7
The Techie Guide to Google Website Optimizer
How Experiments Work
The virtual URL looks like this: “/<experiment key>/test” where the experiment key is the same as
the k variable in the Control Script like var k=’2045836535’.
Detailed Explanation for A/B Experiments
Now let’s take the same technical look at what happens for A/B experiments:
1. The visitor’s browser makes a request for http://www.mysite.com/landing_page.html
2. The contents of landing_page.html are loaded into the browser.
3. The GWO Control Script (at the top of the page) executes.
4. The Control Script looks for a GWO cookie. This is to see if the user has visited the page before.
5. The Control Script makes a request from Google’s servers for an additional script, siteopt.js, and
appends the experiment key and GWO cookie values as such:
http://ww w.google-analytics.com/siteopt.js?v=1&utmxkey=<experiment
key>&utmx=<__utmx cookie value>&utmxx=<__utmxx cookie
value>&utmxtime=<request timestamp>
Know your cookies
Here’s a detailed explanation of the parameters in the GWO cookie:
v The version of the control code making the signup request to siteopt.js. The v value is hard coded in
the Control Script on the test page.
utmxkey The unique identifier for the experiment. This 0-padded 10-digit decimal value is read from the
k variable in the Control Script (var k=’1234567890’).
utmx The value of the ___utmx cookie that GWO uses. It tracks what combinations a visitor has seen for
zero or more experiments. For example:
123456.01234567890123456789:1:1-3-2.98765432109876543210:3:3-1
This example illustrates information for two experiments. The first part (123456 in this example) is
the domain hash, identical to that found in the Analytics cookies (__utma, for example). Then comes
information for experiments, each one separated by at dot. For each experiment, there is a three-part,
colon separated string. The first part is the Experiment ID and Experiment Key represented by a 20
digit number. The Experiment Key represents a family of experiments. Experiment ID uniquely identifies
an experiment, regardless of the family. The second part is for GWO internal purposes. The third is the
combination that the visitor is to see for the given experiment. It is of the form of components separated
by dashes where each component represents the variation chosen for the visitor to see for a given
section. The number of components is equals to the number of sections defined by the experiment. In
the above example, there are two experiments represented. In the first, the visitor is to see combination
1-3-2 and in the second experiment, the visitor is to see combination 3-1.
It’s important to note that information about multiple experiments can be encoded in the utmx cookie.
utmxx This is the value of the __utmxx cookie that GWO uses. This variable is reserved for future use.
utmxtime A simple Unix-based time stamp for the request. This is added so the request will not be
cached.