Random sampling is a technique used in selecting people or or items for research. There are many techniques that can be used; but, each technique makes sure that each person or item considered for the research has an equal opportunity to be chosen as part of the group.
Common Random Sampling Techniques
Random Number Table
Random number tables are created when every person or every item receives a number. The numbers are entered into a table with digits, starting with the number one and including a number for every person or item. The numbers are added onto the table in a random order.
To use this method for random sampling, each person in the population receives a unique number that is included on the table. Numbers are chosen at random from the table. The choice of one digit is unaffected by the choice of any other given digit.
An example of using a random number table is to assign a number to each of 100 people who have expressed interest in attending a special event. Individual numbers are chosen from the random number table. When a person's number is chosen, they are approved to attend the event.
- This is random sampling because any number can be chosen from the table. The numbers don't have to be chosen in numerical order.
- Each number has an equal opportunity to be chosen from the table.
Sampling with replacement is the act of choosing an individual once and then replacing their number or name into the original group of potential people such that the same person has the ability to be chosen more than once.
This procedure is the same as sampling with replacement, except that the name or number of the individual is not replaced into the original group. This results in only one opportunity to be chosen, rather than multiple.
All of the names or assigned numbers of individuals are entered into a given group and then chosen at random.
Using a Computer
Software and other programs are available for the purpose of making random samples.
Real-World Examples of Random Sampling
- At a birthday party, teams are chosen by putting everyone's name into a jar, then choosing names for each team.
- To test the quality of a river's water, samples of the water would be taken from multiple places in the river, on different dates and at different times of the day. All of the samples would be numbered with the numbers entered into a table. As numbers are chosen from the table, quality tests are run on the chosen sample.
- For a study, psychologists assign numbers to all volunteers for the trial. A number table is used to assign volunteers to the control group and to the four test groups.
- To determine what class to put students into at a school, names are entered into a software program, which then randomly places students in each class.
- To determine the quality of items produced on a factory line, a group of produced items would be removed from the line, each receiving a unique number and then the numbers would be entered into a table and selected one at a time until the quality control team has the number of items required for testing.
- At a fundraising event, every attendees name is entered for the chance to win a prize. Names are selected at random, then returned to the jar, giving individuals multiple opportunities to win prizes.
- Students are given an opportunity to win one of five prizes if they have displayed good behavior. Each child who has displayed good behavior throughout the marking period gets one ticket to put into a bowl. Then, five separate names are pulled from the bowl, without replacing them.
- In a warehouse with an assembly line operation, each employee is assigned a random number using computer software. The same software is used periodically to choose a number of one of the employees to be observed to ensure he is employing best practices.
- A company assigns random numbers using a number table to employees. Every week, a number is chosen and that employee is expected to go for blood tests to ensure sobriety.
- A restaurant leaves a fishbowl on the counter for diners to drop their business cards. Once a month, a business card is pulled out to award one lucky diner a discounted dinner.
- An organization uses a computer program to assign numbers to all of their clients. Once a week, the organization uses the computer program to choose a client for the firm to provide lunch for as a reward for their business.
Remember, there are many ways to implement random sampling. What they all have in common is that each person or item has an equal chance to be chosen.