Underestimate Change Fast Study

日期:2015/11/18

A shibboleth on Wall Street and life is that we underestimate change.  I've heard it a million times in popular and academic papers. Zarnowitz adduced it in his study of forecasts 50 years ago also. I felt a fast study might be of interest. Do the big changes following big announcements in the early periods tend to continue or reverse. I tested it for 100 of the biggest changes. As usual the popular view is totally off. There is a big tendency for the big rises to be followed by big declines to an inordinate extent and the same reversal tendency for big declines. The study would have to be expanded to be of merit but it's a much better way of quantifying the effect than the subjective studies festering about.

UPDATE: I found 600 article (items) with the tag "underestimating change stock" on google and many of them are very interesting including an article on underestimating earnings announcement price movements and buying straddles to profit, also analysts not taking account of price changes before earnings announcements in making their predictions. But I didn't come across any that examined a large sample with a definite and non-overlappng data set like mine. My study shows that if you take all the important announcements, and look at the change in the first 10 minutes that are big, there is a significant tendency to reversal. I also looked at all the big 10 minute changes around 830 without regard to the announcement and found the same effect. I can say that at least at the microscopic level, with moves of about 0.2% expected, there is a substantial tendency to overestimate the impact of announcements.