Pop Quiz: 20% Chance of Rain. Do You Need an Umbrella?

This podcast episode explores how people interpret probability. One of the most common encounters with percent probabilities has to do with weather. Take a moment to consider the question below. It comes from a survey developed by scientists at the National Center for Atmospheric Research who were researching how people understand weather forecasts.

Tomorrow's forecast calls for a "20 percent chance of rain." Which of the options below do you think best describes what that means?

A.) It will rain tomorrow in 20 percent of the region.
B.) It will rain tomorrow for 20 percent of the time.
C.) It will rain on 20 percent of the days like tomorrow.
D.) Twenty percent of weather forecasters believe that it will rain tomorrow.
E.) I don't know.
F.) Other

When a select group from the general population was asked this question, some thought a 20 percent chance of rain means you should definitely bring an umbrella, while others said they would be surprised if it even drizzled. And at least one person looked at the question the other way: There was an 80 percent chance it wouldn't rain.

For the National Weather Service (NWS), of course, this is not a question to puzzle over for fun. It's serious stuff. They need the public to not only understand forecasts, but to have confidence in them so that people will respond appropriately to weather threats.

• Access Podcast: Pop Quiz: 20% Chance of Rain. Do You Need an Umbrella? (~7 min)
• Access Transcript: Pop Quiz: 20% Chance of Rain. Do You Need an Umbrella?

This podcast was one of six in a series that focused on how we interpret and communicate probability and uncertainty, produced by All Things Considered, NPR.

Extracted from accompanying podcast description.