What is multivariate testing and when should I use it?

Multivariate testing tests multiple variables simultaneously to understand how different combinations perform. Unlike A/B testing which tests one variable, multivariate testing can test headline + image + CTA combinations, for example. Use it when you want to understand interactions between elements or when you have high traffic and want to test faster. However, it requires much more traffic than A/B testing since you're testing multiple combinations. It's best for pages with very high traffic where you can get statistical significance quickly. For most sites, A/B testing is more practical. Example: A high-traffic e-commerce site used multivariate testing to test 3 headlines × 3 images × 2 CTAs (18 combinations) simultaneously, finding the optimal combination faster than sequential A/B tests.