I. When the sum of the residuals is greater than zero, the data set is nonlinear. II. A random pattern of residuals supports a linear model. III. A random pattern of residuals supports a non-linear model.
bull market definition. A market, especially a stock market, characterized by rising prices; the opposite of a bear market. We can always go back to worrying; we are still in a bull market for fear.
Second, like many others do, they defined bear markets as a 20% decline from a prior peak lasting at least 3 months. They defined bull markets as an advance of 50% or more from the low of a bear market over 6 months or longer. From those definitions and parameters, they conclude the average bull market is 50 months.