Distribution Shapes
由直方图到 smooth curve
1.this distribution of heights is bell shaped(or mound shaped), but the smooth curve makes seeing the shape a little easier.
2.need not worry about minor differences in shape（全局），allows us to classify most distributions by designating
A distribution is unimodal if it has one peak; bimodal if it has two peaks; and multimodal if it has three or more peaks
Symmetric：are mirror images of one another
Key：Distinguishing between data for an entire population（census data.） and data for a sample of a population is an essential aspect of statistics.
The distribution of population data =the distribution of the variable
