These terms generally represent a test design where the tester is able to test multiple experimental variables simultaneously, generating multiple permutations/combinations of those variables. Many different test designs can be used for a multivariable test, including Full Factorial and Fractional Factorial. Multivariable Testing allows for greater flexability and scalability during the test than A/B Testing does. Some pre-planned fractional factorial designs include Taguchi and Plackett-Burman) and Optimal Designs.