A simple MVT example
Say you have 3 factors on a simple web page. A header banner at the top, some text on the left and an image on the right. For each factor you could have 3 different variations (a ‘control’ and 2 alternatives). These tested variations are referred to as ‘levels’ in multivariate testing.
The total number of experiments (the array) in your multivariate test is then calculated by compounding the number of levels for each factor. Sticking with this same example, a web page with 3 factors, each with 3 levels would contain 27 different experiments (3x3x3) as illustrated in this graphic, with blue, orange and green tiles representing the different levels and factors.
The number of levels per factor isn’t always the same of course. A slightly different example, still with the 3 factors (header banner, image, text) could have 4 variations (levels) of header banner and 3 each of the image and text. In this case the total experiments would be 36 (4x3x3).