The standard deviation of the random-walk-with-drift model's errors is simply the standard deviation of the variable's period-to-period change (the so-called "first difference"), which is 1.75 for X2. This is significantly less than the regression standard error for the linear trend model, which is 2.28.
The standard deviation in statistics is a measure of the amount of variation or dispersion in a set of values. A low standard deviation indicates that the values of the set tend to be close to the mean (also known as the expected value), whereas a high standard deviation indicates that the values are spread out over a larger range. The standard deviation of a population or sample and the standard error of a statistic (for example, the sample mean) are not the same thing, but they are related.
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