# Probability Sampling Methods: Multistage, Multiphase, and Cluster Samples

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• 0:06 Probability Sampling
• 0:59 Cluster
• 2:07 Multistage
• 3:46 Multiphase
• 5:36 Lesson Summary

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Lesson Transcript
Instructor: Natalie Boyd

Natalie is a teacher and holds an MA in English Education and is in progress on her PhD in psychology.

How do researchers choose the subjects for their experiments? In this lesson, we'll look at what probability sampling is and three different probability sampling methods: cluster, multistage, and multiphase sampling.

## Probability Sampling

Imagine that you are a psychologist and a large school district has hired you to design a study testing the health and wellness of 9th graders in their district because the school district officials want to know how fit their students are.

You know that you need to find out how healthy the 9th graders in the district are, but the problem is that there are so many 9th graders that you won't have the time or budget to measure the fitness of all of them. How should you proceed? How do you choose which 9th graders to test?

The sample of a study is the group of participants in the study, and it is chosen in a process known as sampling. One of the main types of sampling techniques is probability sampling, which involves choosing your sample randomly.

Let's look closer at three different types of probability sampling: cluster, multistage, and multiphase sampling.

## Cluster

Ok, so you want to measure the fitness of 9th graders in a large school district, but first you have to choose which 9th graders to test. One way that you might do this is through cluster sampling, or choosing a random sample of clusters to test.

Clusters are just natural divisions. For example, one natural division in a school district is at the school level: School A, School B, and so on. Each school becomes a cluster.

Let's say that you decide to choose four of the high schools in the district and use all of the 9th graders in those four schools as your sample. You'd choose the high schools randomly, by flipping a coin or drawing names out of a hat or using a computer program. Once you've chosen your clusters, or schools, you have your sample. Every 9th grader at those four schools will be in your study.

Cluster sampling works well wherever there are natural divisions, or clusters, in a population. Towns in a county, counties in a state, churches in a town - all of these are examples of naturally occurring clusters.

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