The empirical warning is equally striking. Most of the observed differences among industry returns have nothing to do with long-term industry effects; they are due to the random distribution of especially high and low-performing business-units across industries. As will be shown, an FTC industry return must be at least 15.21 percentage points above the mean to warrant a conclusion (95 percent confidence) that the true stable industry effect is positive. Fewer than one in forty industry returns are high enough to pass this test.