Group spacing: (:maximum quantity-minimum quantity)/group quantity

Probability: the result of theoretical calculation represents probability. Theoretically, the number of occurrences of event A/the total number of occurrences.

Grouping with group spacing requires the following steps:

1, determine the number of groups.

Because one of the purposes of grouping is to observe the characteristics of data distribution, the number of grouping should be moderate. If the number of groups is too small, the data distribution will be too concentrated, and if the number of groups is too large, the data distribution will be too scattered, which is not convenient to observe the characteristics and laws of data distribution. The determination of the number of groups should be aimed at displaying the distribution characteristics and laws of data.

In actual grouping, the number of groups can be determined according to the empirical formula proposed by Sturges: k = 1+lgn/lg2, where n is the number of data and the number of groups is an integer of the rounded result. For example, the data in the previous example is: K= 1+lg50/lg2≈7, which should be divided into 7 groups.

2. Determine the interval between groups.

Group distance is the difference between the upper and lower limits of a group, which can be determined according to the maximum and minimum values (i.e. range) of all data and the number of groups divided, i.e. group distance = (maximum-minimum value) ÷ number of groups. For example, in the previous data, the maximum value is 139, and the minimum value is 107, so the group distance = (139- 107) ÷ 7 = 4.6. For the convenience of calculation, the group spacing should be a multiple of 5 or 10.