What Full Factorial is: A multivariate testing method where every small variation of a website is tested. For example, say you have three different elements on your website that you would like to test. If each of the three elements had three different variations, then to perform a full factorial test, you would have 27 (3X3X3) combinations to test. When you consider that each variation needs enough traffic to reach significance that adds up to a lot of traffic. Only a select few websites have enough traffic for a complex full factorial test to achieve significance in a reasonable amount of time.
What Full Factorial is not: Fractional factorial testing, which is a multivariate testing method that only tests a certain number of variations of multiple elements of a website.
Why Full Factorial matters: This method allows you to test a lot of different variations at once. It also produces the purest experiments. However, it is often too slow to reach significance to be a practical website testing method.
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