Prepare frequency distribution tables and draw frequency distribution graphs

Uses of Frequency Distribution Tables and Frequency Distribution Charts

The quotient obtained by directly adding the sum divided by the number of observations is the mean of the set of data.

First, compile the data into a frequency table to find out the frequency of each group of segments. The sum of the lower limits of two adjacent groups of segments can be divided by 2 to calculate the frequency of each group. Use the class mid-value of the segment and substitute the formula (11-2) to find the mean.

Percentile is a position indicator. Arrange the eight observed values ​​from small to large and divide them into 100 equal parts. Each equal part contains 1% of the observed values. Then the value corresponding to the second percentile is called the percentile, represented by user. Among all the data, there are smaller ones than corpses. 2% of the observed values ​​are larger than corpse, with (100-1)% of the observed values. Obviously the median is ie the 50th percentile (P0). Percentile is used to describe the level of a certain percentile position in the observation sequence, and is often used to determine the reference value range (see Section 2 of this chapter). Percentiles can also be used to describe various frequency distribution data. When multiple percentiles are combined, the distribution characteristics of the observed values ​​can be summarized more comprehensively, including central tendency and discrete trend.

direct method

frequency table method

The purpose of standard deviation: 1. The larger the standard deviation, the more dispersed the distribution of variable values, and the less representative the mean, and vice versa: ② Used to calculate the spatial difference coefficient: ③ Used to calculate the standard error: (error plus mean The law of numbers and normal sums 4. The law of estimating the mean and normal distribution