(Diane Donareff/ AP Images for Carnival Cruise Line) 

Think of the last impulse buy you made at the grocery store. Maybe the item was placed at eye level. Or perhaps it was a Snickers bar you saw in the checkout line. Either way, that product was put there by design, not dumb luck, and most of these placements were decided through randomized trials. We talk with Andrew Leigh, author of “Randomistas: How Radical Researchers Changed Our World,” about how these tests affect everyday life and impact the decisions we make.

Three Takeaways: 

• One of the first randomized trials helped find a cure for scurvy. In 1747, physician James Lind separated sailors on the HMS Salisbury into groups, giving each group a different treatment. The remedies included sulfuric acid, seawater, vinegar, and oranges and lemons. Turns out, the Vitamin C-rich fruit cured scurvy, while those taking the other remedies languished. 
• Whether you know it or not, you’ve been part of a randomized trial. Decided not to click on a headline? You’ve been part of a randomized trial. A store’s promotion wasn’t enough to get you in the door? Randomized trial. Leigh says he even chose his book’s subtitle through an online randomized trial.   
• Many people associate randomized trials with testing the effectiveness of drugs and business plans. But politicians and social programs use them, too. One of the most famous is the Moving to Opportunity study, which placed low-income families in high-income neighborhoods. The results were surprising, to say the least. 

More Reading: 

• Want to know more about the Moving to Opportunities study? The Brookings Institution gives it a thorough analysis.  
• James Lind didn’t just find the cure for scurvy. He also discovered how to distill fresh water from seawater.
• Remember when Facebook conducted randomized trials on its users and everyone got really, really mad? The Atlantic looks into what actually happened.