As an Optimization team, we are new to the whole multivariate testing business. We are more than aware that we dont always do things by the book. So when we undertake a multivariate test we dont always adhere to the basic principles of testing.
The biggest rule we tend to ignore is 'Do not tamper with your test'. The trouble is we always have to have an eye on the bottom line. So we are constantly asking ourselves whether what we're undertaking in terms of testing is not impacting upon our sales in a negative way? Are we actually reducing the conversion rate on the website?
My colleague generally monitors what's going on downstream during a test and looks at the basic application submittion rates for our products. If he notices a downturn in conversion rate during the course of a test we get a bit nervous.
Thankfully our multivariate testing tool, Maxymiser allows us to look at how individual variants are performing. If after a period (usually around one week into a test in our case) we start to see a downturn we'll start to examine closely which variants we can 'cull' from the test.
Once we highlight the under-performers we then downweight* them out of the test entirely. This is beneficial for two reasons:
1. You minimise negative impact on conversion and sales.
2. You reduce the number of page combinations in the test.
The lower the number of page combinations the quicker your test period. This is great for us because of the second rule of testing that we frequently ignore 'Allocate enough time for testing'. Basically speaking we run tests for a far shorter period than is recommended.
Most tests, given enough visitor traffic to your site run anywhere from 4 to 10 weeks, or even longer. We tend to have ran tests from 2 to 6 weeks. Our excuse for this is that there is so much other activity going on on the website at any given time by other people that we have a very narrow window in which to test and get a result.
Another key thing when planning your MVT test is knowing how much traffic you get to your site and whether you've got enough traffic to run all your page combinations and see an outright winner at the end of your test. So far we've been reasonably lucky in that we've had enough traffic to run the tests for a relatively short period and still acheive a winner.
Obviously ignoring key testing rules and principles is not recommended. But if lke our Optimzation team, you're stuck between a rock and a hard place, and there's a certain need to get some kind of testing done our early experiences have shown that you can bend the rules to get some kind of learning or outcome in a short space of time.
* In multivariate testing, each variant is usually allocated a weighting. For example, if you give a variant a 50 weighting in the test console it will be served 50% of the time, while the default content is served the other 50% of the time.