Variance s 2 = [(x1-x) 2+(x2-x) 2+... (xn-x) 2]/(n) (x is the average).
The standard deviation formula is a mathematical formula. Standard deviation is also called standard deviation, or experimental standard deviation, and the formula is as follows: standard deviation = arithmetic square root of variance = s = sqrt ((x1-x) 2+(x2-x) 2+... (xn-x) 2)/n).
Extended data:
Standard deviation is the most commonly used quantitative form to reflect the dispersion degree of a group of data, and it is an important indicator to measure accuracy. When it comes to standard deviation, we must first understand its purpose. We use the method to detect it, but the detection method always has errors, so the detection value is not its true value.
The difference between the detected value and the real value is the most decisive index to evaluate the detection method. But what is the real value is unknown. Therefore, how to quantify the accuracy of detection methods has become a difficult problem. This is also the purpose of clinical quality control: to ensure the accuracy and reliability of each batch of experimental results.
Although it is impossible to know the true value of a sample, every sample will always have a true value, no matter what it is. As you can imagine, a good detection method, its detection value should be closely scattered around the real value.
If it is not close, the distance from the real value will be large, and the accuracy will of course be poor. It is inconceivable that the method with large deviation will measure accurate results. Therefore, deviation is the most important and basic index to evaluate the quality of a method.
Baidu encyclopedia-standard deviation