1. Simple Random Sampling
Lecture 7
Section 2.5
Tue, Jan 27, 2004

2. Simple Random Sample
Simple Random Sample of size n – A sample of size n chosen in such a way that all possible samples of size n have the same chance of being selected.

3. Selecting a Simple Random Sample
Given a population of size N, number the members from 1 to N.
Then use a random number generator (such as on a calculator) to generate n random integers from 1 to N.
If the sampling is done without replacement, then repetitions should be discarded.

4. Using a Random Number Table
See the Random Number Table on page 85.
Use it to select a random sample of size n = 10 from a population of size N = 100.
Use it to select a random sample of size n = 10 from a population of size N = 133.

5. Using the TI-83 Press MATH. Use arrow keys to highlight PRB menu.
Press 5 to select randInt (item #5).
Enter randInt(1, 100) and press ENTER.
A random number appears.
Press ENTER repeatedly for more random numbers.

6. Setting the Seed
A random number generator uses a "seed" value to get the next random number. (See p. 87.)
Enter the desired seed, say, 33.
Press STO.
Press MATH, hightlight PRB, select rand (item #1).
Press ENTER. The seed is set to 33.

7. Example
See Example 2.14, p. 88.

8. Let's Do It! Let's do it! 2.4 – A Simple Random Sample of Companies.
Let's do it! 2.5 – Simple Random Sampling.
Divide the class into two groups.
Change “proportion of women” to “proportion of freshmen.”

9. Using Excel Click in Cell A1. Type =rand().
Press ENTER. A random number appears.
Click in Cell B1.
Type =100*A1.
Press ENTER.

10. Using Excel Click in Cell C1. Type =ceiling(B1,1).
Press ENTER. An random integer from 1 to 100 appears.
The functions rand() and ceiling() may be found under “Function…” in the Insert menu.

11. Using Excel Select the rectangle of cells A1 – C1 through A20 – C20.
Press CTRL-D to “fill down.”
Column C now contains 20 random numbers from 1 to 100.

12. Using Excel This could all be accomplished in one column by typing
=ceiling(100*rand(), 1)
in Cell A1 and filling down through Cell A20.
Excel does not give you access to the seed.

13. Assignment
Page 112: Exercises 16 – 21, 23 – 24.