How putting numbers in perspective makes them more memorable

Product & Experience

Two scientists at Microsoft Research, Jake Hofman and Dan Goldstein, believe in this idea so strongly that they’ve spent the better part of a decade spearheading a project known as the Perspectives Engine with a simple goal: develop tools that make numbers easier for humans to understand.

Microsoft’s search engine, Bing, delivers millions of facts a day in response to queries. The Perspectives team wondered whether some simple contextual phrases would help people understand and remember their numerical search results.

So they did something basic: Instead of just reporting that Pakistan has an area of 340,000 square miles, they added a brief “perspective phrase,” something like “that’s about the size of 2 Californias.” And then, at time scales ranging from a few minutes later to a few weeks later, they tested people to see if they remembered the fact they had been shown.

Some perspective phrases were better than others. Simpler comparisons from more familiar states or countries led to better memory for the facts. But ALL phrases were better than nothing. Even a slightly unwieldy comparison was more effective than a number alone.

One million seconds is about eleven and a half days. One billion seconds is nearly thirty-two years. The extra three zeros look modest on the page. In lived time, they separate next week from a different part of your life. That comparison does more than “a thousand times larger” because people have experienced days and years.

Readers can become more confused after a bad perspective phrase. “Twice the size of California” helps someone who knows California, cares about area and can imagine doubling the state. For many British readers it may mean “extremely large, somewhere near films”. We now have precise arithmetic and vague understanding. Choose the reference after choosing the audience and the dimension. Area needs area. Duration needs duration. A charity explaining meals should connect the total to meals per person or contribution. Comparing the food’s weight with an animal merely supplies a cheap headline.

Keep the original figure beside the comparison. Say when the relationship is approximate. Then ask people later what they remember. If they recall California and forget the country, the comparison displaced the fact.

People retain the million-and-billion comparison because they can reconstruct the order of magnitude. They begin to see three zeros as a vast difference. Thirty-two years tends to get their attention.