Extreme difference
Range, also known as range error or range, is expressed by R. R is used to represent the difference between the maximum value and the minimum value of the measure of variance in statistical data, that is, the data obtained by subtracting the minimum value from the maximum value.
It is the maximum range of sign value change and the simplest index to measure sign change. The moving range is one of them. Range can not be used for comparison, the unit is different, variance can be used for comparison, because it is all ratio.
discrepancy
The concept and calculation formula of variance, for example, their scores in five exams are as follows: x: 50, 100, 100, 60, 50, and the average e (x) = 72; Y: 73, 70, 75, 72, 70 Average E(Y)=72. The average score is the same, but x is unstable and deviates greatly from the average. Variance describes the deviation between random variables and mathematical expectations.
A single deviation is the average of the square deviation, that is, the variance without the influence of symbols, which is recorded as E(X): the direct calculation formula separates the discrete type from the continuous type. A calculation formula is also derived: "variance is equal to the average of the sum of squares of deviations of each data and its arithmetic average". Among them, they are discrete and continuous calculation formulas respectively. It is called standard deviation or mean square deviation, and variance describes the degree of fluctuation.