Purposive Sampling 101
What is Purposive Sampling?
Purposive sampling, also known as judgmental, selective, or subjective sampling, is a form of non-probability sampling in which researchers rely on their own judgment when choosing members of the population to participate in their study.
This sampling method requires researchers to have prior knowledge about the purpose of their studies so that they can properly choose and approach eligible participants.
Researchers use purposive sampling when they want to access a particular subset of people, as all participants of a study are selected because they fit a particular profile.
Purposive Sampling vs. Convenience Sampling
The terms purposive sampling and convenience sampling are often used interchangeably, but they do not mean the same thing.
Convenience sampling is when researchers leverage individuals that can be identified and approached with as little effort as possible. These are often individuals that are geographically close to the researchers.
Purposive sampling is when researchers thoroughly think through how they will establish a sample population, even if it is not statistically representative of the greater population at hand. As the name suggests, researchers went to this community on purpose because they think that these individuals fit the profile of the people that they need to reach.
While the findings from purposive sampling do not always have to be statistically representative of the greater population of interest, they are qualitatively generalizable.
The more prior information that researchers have about their particular communities of interest, the better the sample that they’re going to select.
How is Purposive Sampling Conducted?
The method for performing purposive sampling is fairly straightforward. All a researcher must do is reject the individuals who do not fit a particular profile when creating the sample.
However, researchers can use various techniques during purposive sampling, depending on the goal of their studies.
Technique Options Used in Purposive Sampling
Technique options include, but are not limited to, the following.
Typical case sampling is a type of purposive sampling that’s useful when a researcher is looking to investigate a phenomenon or trend as it compares to what is considered typical or average for members of the a population.
Extreme or Deviant
Extreme or deviant case sampling is the opposite of typical case sampling. It is used when researchers want to investigate the outliers from the “norm” when it comes to a particular trend. By looking into these outliers, researchers are able to develop a stronger understanding of behavior patterns in the population.
Critical case sampling is a type of purposive sampling in which one case is chosen for investigation because researchers believe that by investigating it, insights into other similar cases will be revealed.
A maximum variation purposive sample is also referred to as a heterogeneous purposive sample. Researchers use this technique when they are looking to examine a diverse range of cases that are all relevant to a particular phenomenon or event. This allows researchers to gain as much insight from as many angles as possible.
A homogenous purposive sample is the opposite of a maximum variation purposive sample, as it is selected because members of the sample have a shared characteristic or a shared set of characteristics.
Benefits of Purposive Sampling
Purposive sampling enables researchers to squeeze a lot of information out of the data that they have collected. This allows researchers to describe the major impact their findings have on the population.
Purposive sampling is a popular method used by researchers due to the fact that it is extremely time and cost effective when compared to other sampling methods.
Further, the numerous technique options outlined above make purposive sampling a versatile research method that can be tailored to enhance a study’s effectiveness.
Sometimes purposive sampling may be the only appropriate method available if there are a limited number of primary data sources that can contribute to the study.
Drawbacks of Purposive Sampling
The primary downside to purposive sampling is that it is prone to researcher bias, due to the fact that researchers are making subjective or generalized assumptions when choosing participants.
When researchers need to ensure that they are eliminating as much bias as possible, they are better off using a form of probability sampling.
However, researcher bias is only a real threat to a study’s credibility when the researcher’s judgements are poorly considered, or when they have not been based on clear criteria.
For a similar reason, it can be difficult for researchers to convince others that their study has significant representativeness of the larger population of interest.
Due to the fact that researchers are using their personal judgement to select participants and units of measurement, it can be a challenge to convince an audience that if different options were used, the overall findings would still hold true.
The next time you set out to perform a study, consider whether purposive sampling can benefit you, or if you’d be better served using a more traditional, probability sampling method.
Have you had success with purposive sampling? Which technique did you use? We’d love to hear your story. Feel free to drop us a line in the comments below!