Variance is a measure of dispersion when probability theory and statistical variance measure random variables or a set of data. It is used to measure the deviation between random variables and their mathematical expectations.

2. Average difference

The average difference is one of the numerical values indicating the degree of difference between variable values. Refers to the arithmetic mean of the absolute value of each variable value deviating from the average value.

3. Standard deviation

The standard deviation is the square root of the arithmetic mean of the mean square deviation, expressed by σ. The standard deviation is the arithmetic square root of variance. The standard deviation can reflect the degree of dispersion of the data set.

Extended data:

First, the nature of variance:

1. Let c be a constant, then D(C) = 0 (constant has no fluctuation).

2.CX = C2？ D(X) (constant square extraction).

Second, the characteristics of the average difference:

The greater the average difference, the greater the difference between each symbol value and the arithmetic mean, and the smaller the representativeness of the arithmetic mean; The smaller the average difference, the smaller the difference between each symbol value and the arithmetic average, and the greater the representativeness of the arithmetic average.

Third, the calculation method of standard deviation:

Subtract the sum of squares of all numbers, divide the result by the number of this group (or the number MINUS one, that is, the variance), and then find the root. The number is the standard deviation of this group of data.

References:

Variance _ Baidu Encyclopedia

Average difference _ Baidu Encyclopedia

Standard deviation _ Baidu Encyclopedia