You've probably heard the conventional wisdom that Mondays are far and away the best performers in the stock market.  If memory serves, I believe one stat shows that all the net profit can be traced to that one day.  My inclination upon hearing something like that is, “Fine.  Let's test it.”  Here are the last five year results of buying on the opening, selling on the close.

Yipes!  We've found another anti-indicator!  We should be selling on Mondays.

This is obviously a phenomenon of recent history.  I can vouch for the Monday buy rule holding up before�"perhaps another testimonial to the idea of too many people trying to do the same thing.

But wait a minute.  Despite our results, further tinkering reveals something quite interesting.  Actually, a number of Mondays, about half of them, should be bought.  The determining factor is the previous trading day's (usually Friday's) activity.

Here's the rule.  If it's Monday and the previous trading day was up (close to close) then buy today.  If you're following a down day, then be a Monday short seller.

Quite a difference, wouldn't you say?  This is maybe an example from my old mentor and author of the yearly pro football statistics bible Point Spread Playbook Al O'Donnell, who contends that having only some of the information could be more detrimental to your financial health than having none of it.

I can't show you a corresponding bias in the other financials, but common sense should tell us not to expect one.  This is strictly keyed to the psychology of investing around the weekend�"adding to or exiting from a portfolio after a couple day's worth of fear and greed related reflection.  Obviously, the same emotions aren't going to center on, say, two currencies floating against each other.

In the next few postings, we'll see if the calendar can teach us anything else.