Some 52 Years Ago, from Victor Niederhoffer
Some 52 years ago I studied the Friday down Monday down effect, a tendency for Monday moves to be inordinate bad after Friday declines. The z's for it were about -15 for the preceding 25 years. It seemed appropriate to update it. I found that the last 469 Friday declines were followed by an average move of 001 on a base of 15000 with the last 512 Friday rises followed by an average move of 002.
Those are moves of 1/100 of 1%. The standard deviation was about 50% higher at 180 for the Monday moves following the Friday declines showing a significant increase in volatility following Friday declines. That's all that's left of a regularity that is still extant in many of the book.