Submission + - Study Says People Don't Understand Rain Forecasts 1
Hugh Pickens writes: "Cognitive Psychologist Susan Joslyn writes that many 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. "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," Joslyn says. To probe people's understanding of the term 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. Each student only saw one icon or "precipicons," that is visual representation of the chance of rain and forecast, and filled out a questionnaire. Two of the questions asked how much of the time it would rain and over approximately what area of the region would it likely rain today. The correct answer for both questions was "can't tell from this forecast," and only 43 percent of the students correctly responded to both questions. Joslyn says that if the misunderstandings uncovered in this research exist among a college-educated group of students from the Pacific Northwest, where it frequently rains, then similar error probably occur in similar, or larger, numbers elsewhere among the general public. "In dealing with a forecast about rain people must simultaneously consider several hypothetical outcomes, their corresponding levels of uncertainty and their consequences. For some people it may be easier to commit to a single outcome, reducing cognitive load, and proceed as through the uncertainty has been resolved. In some cases they may not be aware of this simplification.""