Here is a survey question some 10,000 investors have answered over the last 26 years; now it’s your turn to try: “What do you think is the probability of a catastrophic stock market crash in the U.S., like that of Oct. 28, 1929 or Oct. 19, 1987, in the next six months? (An answer of 0% means that it cannot happen, an answer of 100% means it is sure to happen.)” For historical context, the 1929 crash saw stocks dive by 13% in one day. Stocks tumbled by 23% in the 1987 crash. So what percentage do you assign to the probability of a similar crash between now and November? According to new research by two famous finance professors at Yale, Robert J. Shiller and William N. Goetzmann, assisted by Dasol Kim of Case Western Reserve, your answer is likely to be colored both by the stock market’s trend over the last few...