用图表描述统计

变量的图表描述

分类变量

(Relative) Frequency Distribution

表格，左侧展示 classes/groups，右侧展示占比，relative frequency distribution: $\frac{\text{frequency}}{n}\times 100\%$

Bar Chart

height of bars 表示 frequency 高低

Pie Chart

focus on proportion of frequency

Pareto Diagram

bar chart that displays the frequency of defect causes, to separate “vital few” from “trivial many”.

Pareto $80-20$ Rule

Cross Table

describe relationships between categorical or ordinal variables

Cluster (Component) Bar Chart

to picture the information in cross tables

数值变量

Frequency Distributions

1. 先确定分类的数量 $k$
2. 然后确定每一个类的步长（需要相同） $w=\frac{\max-\min}{k}$
3. inclusive and nonoverlapping: each observation must belong to one and only one class

(Relative) Cumulative Frequency Distributions

Histogram

Ogives

Scatter Plots 散点图

Shape of Distribution

对称分布

• 左右平衡

偏态分布 skewed

• 右偏（正偏） skewed-left
• 左偏（负偏） skewed-right

Stem-and-Leaf