Sampling question #5: How do I draw a simple random sample?
There are free random number generators on the internet that you can use. Two are: www.random.org and www.randomizer.org
If you want to draw your own sample, there is a method you must abide by in order for your sample to be representative of the population.
1. The first step is to identify all of the members in your population. You must be able to list them in what is called a sampling frame. The frame should have the names without order to them and non-overlapping (no duplicates). Alphabetizing the list by surname is a way to insure a random order in the sampling frame.
2. Second, you must give each name an identification number. Start with “1” and continue.
3. Third, you must decide what the size will be for your sample. You can use the table suggested in the Krejcie (1970) article, or whatever feels right for you to believe in the results you obtain. As a rule of thumb, use as large a sample size as possible.
4. Fourth, you need to get a Table of Random Numbers. Many are located at the end of statistical or mathematical textbooks. The Table of Random Numbers consists of rows and columns of numbers arranged at random so that they can be used as any point by reading in any direction left or right, up or down. We are now ready to draw our random sample.
Here is a simple example for you.
Sampling Frame
ID Name
1. Alex
2. Allen
3. Lea
4. Joey
5. Auggie
6. Mary
7. Ellen
8. Emily
9. Felice
10. Juan
11. Julia
12. Ruthie
13. Annie
14. Mark
15. Miguel
16. Maura
17. Olivia
18. Rachael
19. Rebecca
20. Seth
Fifth, we know that our largest ID number has two digits (20). So we are going to need a two-digit column in the Table of Random Numbers. We start anyplace in the Table of Random numbers. We have decided in advance whether we would use two digits going up, down, left or right. So we begin.
Sixth, Number #6 is the first ID number that is within our band of between 1 and 20. This is the first member of our random sample and it is Mary. We continue 82, 56, 96, 66, 46 until we and come up with the next is ID #13 Annie. Our three last members of the sample are ID #8 (Emily), ID #5 (Auggie) and ID #4 (Joey). We have five randomly selected members: Mary, Annie, Emily, Auggie and Joey.
