本章指南：分析数据需要做的第一步就是进行描述统计。描述统计是用来整理、概括和简化数据的统计方法。在描述统计中，我们可以运用次数分布来将数据分门别类进行整理。本章我们将学习次数分布表、次数分布图、次数分布的形状并掌握百分位数、百分位等级和插值法。
Guide：The first step in analyzing data is to conduct descriptive statistics. Descriptive statistics is a statistical method used to organize, summarize, and simplify data. In descriptive statistics, we can use frequency distribution to categorize and organize data. In this chapter, we will learn about the frequency distribution table, frequency distribution map, the shape of frequency distribution, and master percentile, percentile rank, and interpolation.

学习要点(Learning Points)：

1. 学会作次数分布，累计次数分布，和分组次数分布表；
   Learn to draw frequency distribution, cumulative frequency distribution, and grouping frequency distribution tables;
2. 学会用茎和叶图，直方图，棒图，线图表达次数分布；
   Learn to use stem and leaf charts, histograms, bar graphs, and frequency distribution ploygons to show frequency distribution;
3. 了解正偏态分布和负偏态分布；
   Understand positive skewed distribution and negative skewed distribution;
4. 掌握百分位数和插值法。
   Master percentiles and interpolation methods.

目录

1. 次数分布表 (Frequency distribution table)
2. 次数分布图 (Frequency distribution map)
3. 茎和叶图 (Stem and leaf display)
4. 次数分布的形状 (The shape of frequency distribution)
5. 百分位数，百分位等级，插值法 (percentile, percentile rank, and interpolation)

作业

1. 2023第二章作业 (Chapter 2 homeworks of 2023)
2. 2024第二章作业(Chapter 2 homeworks of 2024)