Do interactions exist in marketing experiments? Though mathematically possible, interactions tend to be small and often non-existent (though inconsistent creative execution can lead to unwanted interactions). However, if an interaction effect is statistically significant, then it can change your predicted lift or even change the optimal combination. For example, if the 1×2 interaction is large, the hero and headline interact. Maybe both are positive, but the interaction is negative, so the new hero + new headline & copy may not give you as much a lift as predicted by the sum of both main effects.

Read more: https://www.linkedin.com/pulse/accelerated-experimentation-testing-15-elements-one-test-gordon-bell-sinkf/