Variance: the value obtained by subtracting the average value from each value in this set of data, squaring these values one by one, adding them together, and then dividing them by the number of data. The obtained value is variance, which is the most commonly used way to describe data fluctuation. The smaller the variance, the smaller the fluctuation, and vice versa.

Standard deviation: it is the arithmetic square root of variance, that is, variance has a root sign.

Average difference: the absolute value of the difference between all values of this set of data and their average values. These absolute values are added and divided by the number of data, and the average value is the average difference.

Quartile deviation: arrange all data from small to large and divide them into four equal parts according to quantity. The sum of the four parts is Q 1, Q2, Q3 and Q4 respectively. The upper part is Q2-Q 1 and the lower part is Q4-Q3. The value obtained by subtracting the lower part from the upper part is called quartile deviation. The smaller the quartile deviation, the more concentrated the data in the middle part. The larger the quartile, the more dispersed the data in the middle part.