Qualitative research employs what is generally called purposeful sampling, which is the intentional selection of individuals to better understand the central phenomenon. Under purposeful sampling there are several ways of selecting individuals for a qualitative study. Below are some examples discussed in this post.
- Maximal variation
- Extreme case
We will also look at suggestions for sample size.
Maximal Variation Sampling
Maximal variation involves selecting individuals that are different on a particular characteristic For example, if you are doing a study on discrimination, you might select various ethnicities to share their experience with discrimination. By selecting several races you are ensuring a richer description of discrimination.
Extreme Case Sampling
Extreme case sampling involves looking out outliers or unusually situations. For example, studying a successful school in a low-income area may be an example since high academic performance does not normally correlate with low income areas.
Theory sampling involves selecting people based on their ability to help understand theory or process. For example, if you are trying to understand why students drop out of school. You may select dropout students and their teachers to understand the events that lead to dropping out. This technique is often associated with grounded theory.
This approach involves selecting several members from the same subgroup. For example, if we are looking at discrimination at a university, we may select only African-American English Majors. Such an example is a clear sub-group of a larger community.
Opportunistic sampling is in many ways sampling without a plan or starting with on sampling method and then switching to another because of changes in the circumstances. For example, you may begin with theory sampling as you study the process of dropping out of high school. While doing this, you encounter a student who is dropping out in order to pursuit independent studies online. This provides you with the “opportunity” to study an extreme case as well.
Sometimes it is not clear who to contact. In this case, snowball sampling may be appropriate. Snowball sampling is an approach commonly used by detectives in various television shows. You find one person to interview and this same person recommends someone else to talk to. You repeat this process several times until an understanding of the central phenomenon emerges.
Qualitative research involves a much lower sampling size then quantitative. This is for several reasons
- You want to provide an in-depth look of one perspective rather than a shallow overview of many perspectives.
- The more people involved the harder it is to conduct the analysis.
- You want to share the complexities rather than the generalizations of a central phenomenon.
One common rule of thumb is to collect data until saturation is reached. Saturation is when the people in your data begin to say the same things. How long this takes depends and this is by far not an absolute standard.
This is just some of the more common forms of sampling in qualitative research. Naturally, there are other methods and approaches to sampling. The point is that the questions of the study and the context shape the appropriateness of a sampling method.