The standard deviation SD, also often called the mean square deviation, is different from the mean square error, which is the average of the square of the true value of each data distance, that is, the average of the sum of the squares of errors.

The formula is close to variance in form, and its root is called root mean square error, which is close to standard deviation, and the standard deviation is the square root of the average sum deviating from the mean square, which is 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. If the average value is the same, the standard deviation may be different.

SD is a non-negative value, which is the same as the unit of measured data. There is a difference between the standard deviation of a population or random variable and the standard deviation of the number of samples in a subset.

The standard deviation formula is a mathematical formula. Standard deviation is also called standard deviation, or experimental standard deviation.

Standard deviation calculation formula: standard deviation σ = square root of variance.

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).

Extended data:

Pythagorean theorem, formerly known as Pythagorean string theorem. The content is that in a right triangle, the sum of squares of two right-angled sides = the square of the hypotenuse. The formula is: Goufang 10 layer square = chord square.

According to the degree of the internal angle of a triangle, it can be divided into three types: right triangle, acute triangle and obtuse triangle.

Arithmetic square root: Generally speaking, if the square of a positive number X is equal to A, that is, x2=a, then this positive number X is called the arithmetic square root of A ... In particular, we stipulate that the arithmetic square root of 0 is 0.

Square root: Generally speaking, if the square of a number X is equal to A, that is, x2 = a ... then this number X is called the square root of A, also called the quadratic root. Positive numbers have two square roots; 0 has only one square root, which is 0 itself; Negative numbers have no square root.

A positive number has two square roots, one is the arithmetic square of A, and the other is-,which are opposite. Together, these two square roots can be recorded as positive or negative.