This week’s best investment advice: Ignore the initial reports on how well or poorly retailers are faring. That’s because those initial reports at best are worthless as a guide to how retailers, and the stock market as a whole, will do from now until the end of the year. And they may even be worse than worthless, as the stock market in December often moves in the opposite direction to how it does right after Thanksgiving. Consider what I found when comparing the Dow Jones Industrial Average’s DJIA, -0.27% performance on the Friday after Thanksgiving—aka Black Friday—with its return from then until the end of the year. This chart shows what my PC’s statistical program spit out; it reflects data back to the mid-1970s, which (as far as I have been able to discover) is when the phrase “Black Friday” began to be used to refer to the big shopping day on the Friday after Thanksgiving. (The data for years before 1975 tell the same story, by the way.) Notice the inverse correlation in the chart: The Dow gains more after declining on Black Friday than it does after rising.via