National EMSC Data Analysis Resource Center
When each eligible subject has the same probability of being selected for inclusion in your sample, it is called ‘simple random sampling.’
For example, suppose a school administrator over 4 schools wishes to find out students’ opinions about food served in the school cafeterias. (S)he has a complete list of all students in the schools and decides to randomly select 150 students from the list.
In this example, each student throughout the 4 schools has an equal probability of selection to be given the survey; therefore, it is a simple random sample.
As the name implies, selecting a simple random sample is, well… simple!
A small catering business serves 9 reception centers. The owner wants to interview a sample of 4 clients in detail to find ways to improve services to his/her clients. To avoid bias, the owner chooses a simple random sample of size 4.
Each reception center is assigned a numerical label 1-9.
1 - Darlene’s Wedding Center
2 - Magic Moments Reception Hall
3 - Rustic Realm Weddings
4 - Romance Gardens
5 - Classic Weddings
6 - Old Time Chapel
7 - Lovers Lane Weddings
8 - Accents-Modern Weddings
9 - Century Falls Reception Center
The owner decides to use a statistical software program to generate 4 numerical labels between 1 and 9 at random. The software returns the following numbers:
5, 8, 6, 4
Therefore, the simple random sample to be interviewed in detail will be:
- Classic Weddings (5)
- Accents-Modern Weddings (8)
- Old Time Chapel (6)
- Romance Gardens (4)
Contact a NEDARC statistician for help with simple random sampling.