[Member (365WT)]answers [Chinese ]  Time :20190401  The variance is the average of the sum of the squares of the deviations of the individual data from their arithmetic mean, usually expressed as σ2. The measurement unit and dimension of variance are inconvenient to explain in an economic sense. Therefore, in the actual statistical work, the arithmetic square root of the variance, the standard deviation, is used to measure the degree of difference in statistical data. Variance and standard deviation are the most important and most commonly used indicators of the degree of variation in the measurement data.
The standard deviation is also called the mean square error and is generally expressed by σ. The calculation of variance and standard deviation is also divided into a simple average method and a weighted average method. In addition, the formula is slightly different for the overall data and the sample data. The variance is the average of the square of the difference between each data and the mean. For example, 1.2.3.4.5 The average of the five numbers is 3, so the variance of the five numbers is 1/5[(13)2 (2 3)2 (33)2 (43)2 (53)2]=2
1\n[(x1x average)^2 (x2x average)^2............ (xnx average)^2] 
