Using the method from the previous question, you have found the design that maximizes savings. However, before you roll out the product across the rest of the country, you decide that you should make sure that this product actually makes people better off and doesn't cause them to save too much. What method should you use to do this? A standard randomized controlled trial ("RCT") Rapid-fire tests ("RFTs" or "A/B testing") A difference-in-differences design ("DiD") A needs evaluation