As is the case every January, the financial media try to draw conclusions for the remainder of the year based upon the first few trading days. These studies are so popular that two phrases have been coined to describe them – "as goes the week, so goes the year"� and, "as goes the month, so goes the year."� Do these adages have a basis in fact?

As Goes the Week . . .

The table below shows the historical record of the S&P 500. We defined the first week of the year as the first 5 trading days in January.

The top panel of the table shows all weeks as a predictor of the following 51 weeks. The bottom panel shows the same indicator using only the first week of every year to predict the following 51 weeks.

Since 1928, if the S&P...