People's misperceptions cloud their understanding of rainy weather forecasts

[OKIsItJustMe]

http://www.eurekalert.org/pub_releases/2009-04/uow-pmc041409.php

Public release date: 14-Apr-2009

Contact: Joel Schwarz
[e-mail]
206-543-2580
University of Washington

People's misperceptions cloud their understanding of rainy weather forecasts

If Mark Twain were alive today he might rephrase his frequently cited observation about everyone talking about the weather but not doing anything about it to say, "Everyone reads or watches weather forecasts, but many people don't understand them."

He'd do that because new research indicates that only about half the population knows what a forecast means when it predicts a 20 percent chance of rain, according to researchers at the University of Washington.

Writing in the Bulletin of the American Meteorological Society, the researchers said the confusion comes because people don't understand what the 20 percent chance of rain actually refers to. Many people think it means that it will rain over 20 percent of the area covered by the forecast or for 20 percent of the time period covered by the forecast, said Susan Joslyn, a UW cognitive psychologist and senior lecturer.

"When a forecast says there is 20 percent chance of rain tomorrow it actually means it will rain on 20 percent of the days with exactly the same atmospheric conditions," she said. "With the exception of the probability of precipitation, most weather forecasts report a single value such as the high temperature will be 53 degrees. This is deterministic because it implies that forecasters are sure the high temperature will be 53 degrees. But forecasting is probabilistic and 53 degrees is in the middle of the range of possible temperatures, say 49 to 56 degrees."

To probe people's understanding of the more familiar probability of precipitation, a technique used in public forecasts since the late 1960s, Joslyn and her colleagues tested more than 450 Pacific Northwest college students in three experiments.

…

If college students don't understand the implications of weather forecasts, how can we hope that they will understand the implications of climate forecasts?

[phantom power]

1. Remember...

it's perfectly possible, depending on your major, to graduate from college without any statistics or science.

For that matter, it's also possible to pass a statistics or science class without understanding or retaining very much of it.

[OKIsItJustMe]

5. "A 20% chance" really doesn't take much math or stats to comprehend

On the other hand, I know "reasonable" people who buy lottery tickets.

Our state lottery's motto is, "Hey, you never know!"


Well, no, I guess I don't, but I've got a pretty good idea…

[Sal Minella]

6. Ya. Have never bought a ticket -- I figure I'll get struck and killed by a falling meteorite

before my ticket wins.

[xxqqqzme]

2. here in SoCal, in the last 10 days

rain was predicted on 5 days. It was 100% wrong. I have to go water my garden now.

[Rabrrrrrr]

3. Always good to remember that most people are stupid; and willingly, celebratorially so.

And this country is so math (especially in prob and stats) and science illiterate that calling it "math and science illiterate" gives it too much credit by implying that there may be some minimal amount of math or science literacy in the average person to begin with.

[hobbit709]

4. If my dog isn't hiding in the bathtub

It ain't gonna rain no matter how many severe weather warnings on the TV screen. She gives a 60-90 minute warning and so far has been about 6 times more accurate than our local weather terrorist as I call him.