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What is purposive sampling?

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One of the most important aspects of any market research study is finding the right audience to survey. If it’s a specific audience, you might need to survey hundreds or thousands of respondents to collect a meaningful sample from the right people.

Sometimes, a study is focused on a very targeted group of people with specific attributes that can respond to a relevant set of questions. For this type of study, researchers can use purposive sampling, where they rely on personal judgment when choosing people to respond to a study.

This article will give you in-depth knowledge about what purposive sampling means, how it’s used, and how to make it work for your business. You’ll also be prepared to overcome some of its limitations with examples of use cases. When purposive sampling is used the right way, you can generate quality data in a short amount of time. 
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What is purposive sampling? 

What does purposive sampling mean? 

The term has several names: judgmental sampling, subjective sampling, and selective sampling. Purposive sampling is when a researcher selects a population sample based on their judgment, knowing they can find a representative sample to conduct their research. It’s an analyst’s intuitive selection of a sample population for primary market research

The success of purposive sampling is contingent upon the researcher’s knowledge and their ability to reach eligible participants. The more they know about the research topic, the better their chance of acquiring accurate results from their sample audience. Lack of information will result in an unfocused investigation rendering a correlation between relevant and irrelevant findings. 

For example, let’s say a food services company is trying to understand whether female college students will respond positively to vegan menu items. The simplest form of purposive sampling might be to visit a local university and poll female students on the street, or post a QR code for an online survey in the women’s restrooms. But this method would only give you results from a single, local market, and potentially include women who don’t live on campus or take advantage of food services. 

Another purposive sample might be to target female college athletes, which would provide a national sample of women who eat on campus, are likely more focused on nutrition, and more inclined to provide a relevant response.

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Advantages of purposive sampling

Why use purposive sampling? 

Some of the key benefits of purposive sampling is that it delivers fast results and in-depth insights. If you have access to the exact audience you want to target, you won’t have to wait to field a large, more general study in order to collect a representative sample. 

It can also be a cost-efficient way of reaching a niche audience, because you’re only approaching the participants that you believe can provide a relevant response (vs. reaching a broad audience and using filters to get to a meaningful sample). It can be an easy way to execute customized research by allowing you to get deep insights out of a relatively small and specific sample.  

Furthermore, purposive sampling can deliver relevant results and more qualitative research. That’s because the researcher starts off with an audience that already fits the questions, which will likely elicit more meaningful responses.

Limitations of purposive sampling 

There are some downsides of judgmental sampling. Results can be biased because the participants were chosen based on assumptions made by the researcher. The criteria for how and why purposive sampling is selected might seem intuitive for the researcher, but isn’t always clear to other stakeholders. The researcher could be more vulnerable to errors in judgment due to a lack of objectivity. 

Consequently, results rendered from such research might also be biased, and some may question the validity of the results. It may also be challenging to convince stakeholders the results would remain the same if different variables are used. It can also be difficult to generalize the data since the sample was created out of a very specific segment or audience. 

Purposive vs. convenience sampling

Purposive sampling is sometimes referred to as convenience sampling, but they are different. Convenience sampling is when an analyst gets their insights from a source that’s easily accessible to them and requires little effort. Such sources will likely be recurring sources from past investigations and those in close proximity. 

Purposive sampling can be convenient, but the researcher has a more defined purpose in selecting relevant sources. Through purposive sampling, the researcher is more methodical in selecting their sample population, whether it’s one respondent or several. This approach is necessary, so the intended characteristics and traits of the sample population fit the larger demographic profile.  

Use cases 

When is purposive sampling used? 

Researchers will usually select respondents familiar with the case study as part of a sampling. Use cases are also good for choosing experts, introducing a new product or service, analyzing a culture, religion, and academic research.

Choosing experts

Choosing an expert for your purposive research can happen early in the process, when you’re trying to understand the right questions to ask. For instance, a investment first wants to create a more inclusive work environment. As a result, they reach out to a manager who they know has experience implementing inclusivity in the workplace. This provides them with additional expertise needed to create a purposive study that will ask relevant and meaningful questions.

Introducing new products and services 

Purposive sampling is useful for presenting new products and services to the market. For instance, introducing a new diet food into the food and beverage industry needs to understand what will appeal to consumers as well as deliver on best practices for nutrition and weight loss. In this circumstance, the company behind the idea might subjectively sample someone more knowledgeable than itself within the industry who can test the product, like a dietician or food scientist. 

Anthropology

If your investigation involves the anthropology of a culture or religion, you’ll need to consult someone you believe is associated with that field. That association could be based on social, professional, or educational experience. For instance, if a filmmaker wants to produce a movie based on Egyptian culture, they’ll need to research information from people associated with the culture in various ways to produce an authentic project.

Educational groundwork

In education, purposive sampling is used to get student feedback on courses they’ve taken. Administering student feedback and insights can reveal how well an educational program is doing. This feedback is based on their responses about the course material, the instructor, and lesson plans. Purposive sampling is also used when the analyst studies a specific academic department or subject. For example, if a researcher investigates the graduation rate for science majors, they won't need a sample from liberal arts majors.  

How is purposive sampling conducted?

There are 7 techniques that can be used for purposive sampling. The following techniques rely on the researcher's intuitive knowledge to determine who’s most beneficial for the research:

  1. Typical case sampling 

Typical case sampling focuses on the average population within a case, context, event, or place. The researcher avoids including extreme sampling or deviant cases in the study and will compare results with similar typical case samplings. In other words, researchers use this technique when they’re interested in the normality of the units within a case study. 

  1. Extreme or deviant case sampling

Extreme case sampling counters typical case sampling. It’s a purposeful sampling that peers into the anomalies of a case study for a stronger perception of behavioral patterns within a certain population. It’s another way of understanding trends and phenomena. Deviant case sampling can also provide new insights toward future research. 

  1. Critical case sampling

Critical case sampling involves a selective study of an event to gain further insights into another investigation. It can involve multiple investigations to analyze a correlation of events associated with one another. This technique helps make logical generalizations. 

  1. Maximum variation 

Maximum variation is similar to critical case sampling. It’s also known as a heterogeneous purposive sample. The difference between these two techniques is that maximum variation purposely examines the most diverse range of events to compare the phenomenon. This technique will render a wider range of data allowing you to analyze a case study from multiple perspectives.

  1. Homogenous

Homogeneous case sampling counters maximum variation. This purposive sampling technique methodically selects cases that have the same traits. This technique is used when the research addresses specific characteristics of a target group of interest. A homogeneous purposive sampling can be created on any basis. For instance, a study can be categorized into doctors, nurses, or surgeons in the healthcare industry. It can also be by department. For example: pediatric, geriatric, or physical therapy.  

  1. Total population sampling

Total population sampling involves investigating the entire population within a case study. The people within that population will share a specific experience, knowledge, or skill set. Total population sampling is useful for interviewing people who have attended an event like a concert, a conference, or a theatrical outing.

  1. Expert sampling

Purposive sampling does not always require using an expert for your case study, but it can certainly help. In relation to educational groundwork, acquiring experts enables you to become better informed about the research. Expert sampling will also help you come to a more well-informed analysis. 

Examples of purposive sampling

Some examples of purposive sampling in research involve television reporters stopping what seems to be a random person in the streets to interview them. It’s not that random. Reporters must quickly assess who will answer their questions in a way that helps report their story. For example, if they’re looking to interview an eyewitness, the reporter will likely select a participant who was close to the event vs. someone who arrived afterward. 

Another example is attorneys working on a class-action lawsuit, who will do a purposive sampling of people affected by the event, people, company, or site. If a technological issue arises, researchers will gather a sample of highly qualified engineers related to that issue to troubleshoot.

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