For your dissertation research, you will need to choose a sampling method to obtain participants. Choosing an appropriate sampling method is important for both quantitative and qualitative studies. There are two general types of sampling methods: probability sampling and non-probability sampling. In this blog, we will explain these two types of sampling and when it is appropriate to use them.
The first type of sampling is probability sampling, which involves a random or probabilistic process to select participants. The various forms of random sampling (including simple random sampling and stratified random sampling) are probability sampling techniques. In simple random sampling, the study randomly selects every member of the population with an equal chance. Stratified random sampling selects individuals from subgroups to ensure proper representation.
The goal is to obtain a representative sample so the study can generalize its results to the population. The goal is a representative sample for generalizing study results to the population. This is less relevant for qualitative studies that focus on a specific group rather than generalization.
Non-probability sampling, on the other hand, does not involve “random” processes for selecting participants. In non-probability sampling, the study does not select all population members.
This method of convenience sampling, which involves selecting only participants who are readily accessible, is one of the most common. Keep in mind that any procedure where the researcher does not randomly select participants or where participants self-select qualifies as a non-probability sampling method. Even using online survey hosting services like SurveyMonkey or Qualtrics may count as non-probability sampling, as their participant pools may not include every population member or use random processes to select participants.
Non-probability sampling is not ideal for quantitative research because it cannot confidently generalize results to the larger population, unlike probability sampling. However, non-probability sampling is often used in quantitative research because probability sampling is not always feasible. Going back to the college professor example, it may not be possible for you to select a random sample from all possible college professors in the general population. You likely would not be able to compile a list of every single college professor in the population with their contact information.
In these cases, quantitative researchers may resort to convenience sampling. On the other hand, non-probability sampling is well-suited for many types of qualitative research. This is because qualitative research is not always concerned with generalizing the results to a larger population. Qualitative researchers often use purposive sampling, a non-probability sampling technique in which the researcher chooses participants because they have specific expertise or insight regarding the phenomenon of interest.
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