Standard deviation is also called standard deviation or experimental standard deviation, and the formula is as follows:

Sample standard deviation = arithmetic square root of variance = s = sqrt ((x1-x) 2+(x2-x) 2+... (xn-x) 2)/(n-1))

Population standard deviation = σ = sqrt ((x1-x) 2+(x2-x) 2+... (xn-x) 2)/n)

Note: X in the above two standard deviation formulas is the arithmetic average of a group of numbers (n data). When all numbers (number n) appear in probability (the sum of the corresponding n probability values is 1), then X is the mathematical expectation of this group of numbers.

Standard deviation

Because the variance is the square of the data, it is generally too different from the detected value itself, so it is difficult for people to measure it intuitively, so it is often converted back by the root sign of the variance (taking the arithmetic square root). This is the standard deviation (SD) we are going to talk about.

In statistics, the average difference of samples is mostly divided by the degree of freedom (n- 1), which refers to the degree to which samples can be freely selected. When there is only one left, it can no longer be free, so the degree of freedom is (n- 1).

The above contents refer to Baidu Encyclopedia-Standard Deviation Formula.