The problem with such predictions (likewise stock market) is that they are not binary. The question is not if a stock goes up or down. The question is "when?". There is no such thing as "opposite" of a date (in a useful sense).

There is actually another questions "how much?". There is also no opposite for that.

But many predictions ARE basically binary. I made so much money on the "Will Trump be impeached by the end of 2019?" question. I can't believe how many people put money on that.