It certainly makes a difference. We looked at several indexes and ETFs. It shows the performance on each weekday (Mondays, Tuesdays, Wednesdays, Thursdays, and Fridays). The results are quite interesting as there is quite a difference for a couple of specific days of the week.
The table below shows the performance of the Dow30 (through DIA), SP500 (through SPY), XLF, EWZ (Brazil), XFI (China), and the SP500 itself. The SP500 closely follows the Dow30 as they are highly correlated (see our post on correlation).
(Click on image to enlarge)
If you guessed one of them was Fridays, you are correct. Fridays are very good days to go short, most likely because people do not want to leave money on the table for unexpected bad news on the weekend?). The Dow 30 has gone down on 19 out of 25 Fridays for the first half of this year from January 2 2008 to June 30 2008. The average daily performance on Friday was -0.69%. If you shorted the Dow index at the end of the day on Thursdays and sold it at the end of the following day on Fridays, your cumulative performance would have been -15.95%. In comparison, the total return for the 6 months was -12.21%.
Note also that since the start of the year Brazil gained 10.3%, while its performance on Fridays was a cumulative -7.19%.
As for the best days to go long, it is clearly Mondays, where the Dow has gained 3.88% in spite of what was clearly a bear market in this first half of 2008.
The table also shows the number of days with returns over +0.5% and under -0.5%.
The graph below shows the performance of the Down on each weekday. You can clearly see how people usually sell on Fridays, perhaps afraid of whatever bad news might come on the weekend.
The Excel file used is also available for your viewing pleasure.
