High Quality Content by WIKIPEDIA articles! Popular Science Predictions Exchange (PPX) was an online virtual prediction market run as part of the Popular Science website. The application was designed by the same group behind the Hollywood Stock Exchange using their virtual specialist application. Users traded virtual currency, known as POP$, based on the likelihood of a certain event being realized by a given date. Stock prices would range between POP$0 and POP$100 and were intended to reflect the general confidence of the users about that event. A stock at price POP$95 would mean roughly that users believed there to be a 95% chance of the event happening. If an event was realized by the given date, the stock will pay out POP$100 per share. A stock that did not occur by the closing date was worth POP$0 per share.