# Lecture_3
Author: Zheyuan Wu
Date: 2023-01-23

#### Zheyuan Wu

#### 2023-01-23

## Example from last class

To select representative sample when there is groups of people:

- Separate sample to different group (eg.SRS of size 80 from group from 800 Group A, then 15 from group from 150 Group B..)

- Combine all 3 groups to get 100 clients <- stratified sampling.

### In R

    y1 = sample (seq(1,800),size=80)
    y2 = sample (seq(801,950),size=15)
    y3 = sample (seq(951,1000),size=5)
    # in R, you may use c() to represent array.
    y = c(y1,y2,y3)

statistical population

v_i_ = response from the ith client in the population v_i_ = {1:yes,0,no} statistical population = {v_1_,v_2_,…v_1000_}