If memory serves, last year, before Christmas, there was a big sell off. ??
Just checked
the S&P for the past year and it seems right before Christmas stocks tanked, and then they soared in the week after. The only 'calendar effect' that I count on is the fact that since most stocks are traded by institutions and their managers have to please others, that they tend to buy/sell at the last minute before the reports are due to make what they got look good. That means at the end of the year (end'o'quarter too sometimes) we get a lot of turmoil that goes nowhere. Right after reports go out it all goes back the way it was --so it seems.