Research Sampling

# Non-probability Sampling – Types, Methods and Examples

## Non-probability Sampling

Definition:

Non-probability sampling is a type of sampling method in which the probability of an individual or a group being selected from the population is not known. In other words, non-probability sampling is a method of sampling where the selection of participants is based on non-random criteria, such as convenience, availability, judgment, or quota.

### Non-probability Sampling Methods

Non-probability Sampling Methods are as follows:

#### Convenience Sampling

This method involves selecting individuals or items that are easily accessible or convenient to the researcher. For example, a researcher conducting a study on college students may select participants from their own class or dormitory because they are convenient to access.

#### Snowball Sampling

This method involves selecting individuals who know other individuals who meet the criteria for the study. The researcher starts with a few participants and then asks them to refer others who may be interested in participating. This method is often used in studies where the population is difficult to access or identify.

#### Quota Sampling

This method involves selecting a sample that matches the characteristics of the population. The researcher sets quotas for each characteristic (such as age, gender, or occupation) and selects participants who fit into those quotas. This method is often used in market research studies.

#### Purposive Sampling

This method involves selecting individuals or items that meet specific criteria or have specific characteristics that the researcher is interested in studying. For example, a researcher studying the experiences of cancer survivors may purposively select individuals who have undergone chemotherapy.

#### Volunteer Sampling

This method involves selecting individuals who volunteer to participate in the study. This method is often used in studies where the population is difficult to access or identify.

### How to Conduct Non-probability Sampling

To conduct a non-probability sampling, you should follow these general steps:

• Identify the target population: Identify the population you want to study. This can be a specific group of people, a geographic location, or any other defined population.
• Determine the sampling method: Choose the non-probability sampling method that is most appropriate for your study. Consider the advantages and disadvantages of each method and select the one that fits your research question and resources.
• Determine the sample size: Determine the appropriate sample size based on your research question, the available resources, and the sampling method you choose.
• Recruit participants: Recruit participants using the selected non-probability sampling method. For example, if you are using convenience sampling, you might approach people in a public place to participate in your study.
• Collect data: Collect data from the selected participants using the appropriate research methods, such as surveys, interviews, or observations.
• Analyze the data: Analyze the data collected from the sample to draw conclusions and make generalizations about the population.

### Examples of Non-probability Sampling

• Convenience Sampling: In this type of sampling, participants are chosen because they are easy to reach or are readily available. For example, a researcher may choose to survey the first 100 people who enter a shopping mall.
• Quota Sampling: Quota sampling is a type of non-probability sampling in which participants are selected to ensure that the sample reflects the characteristics of the population in terms of certain traits. For example, if a researcher wants to conduct a study on the opinions of men and women about a certain product, they may select a sample that has an equal number of men and women.
• Purposive Sampling: In this type of sampling, participants are selected based on specific criteria such as age, gender, occupation, or experience. For example, a researcher may choose to interview only CEOs of Fortune 500 companies to study their leadership style.
• Snowball Sampling: Snowball sampling is a type of sampling in which the initial participants in a study are asked to refer others who they know that fit the criteria of the study. For example, a researcher may ask a person who has experienced homelessness to refer others they know who have experienced homelessness for a study on homelessness.
• Judgmental Sampling: In judgmental sampling, the researcher selects participants based on their own judgment about who would be the most appropriate for the study. For example, a researcher may select participants for a study on the effects of a new cancer drug based on their experience with the disease and their likelihood of benefiting from the treatment.

### Applications of Non-probability Sampling

Here are some applications of non-probability sampling:

• Exploratory Studies: Non-probability sampling is commonly used in exploratory studies where the focus is on generating new ideas and insights rather than testing hypotheses. Exploratory studies often use a small sample size, and non-probability sampling is used to identify potential patterns or trends.
• Pilot Studies: Non-probability sampling is also used in pilot studies, which are small-scale studies conducted to evaluate the feasibility and potential outcomes of a larger study. Pilot studies often use a convenience sample or purposive sampling to identify potential issues or areas of improvement before conducting the larger study.
• Qualitative Research: Non-probability sampling is commonly used in qualitative research where the focus is on gaining an in-depth understanding of a particular phenomenon or context. Qualitative research often uses purposive sampling to identify participants who have the knowledge or experience needed to provide rich and detailed insights.
• Rare Populations: Non-probability sampling is used in studies of rare populations, where it may be difficult to obtain a large enough sample using a random sampling method. Snowball sampling is often used in studies of rare populations to identify potential participants through referrals from existing participants.
• Convenience Sampling: Non-probability sampling is also used in studies where the sample size is not a critical factor, and the focus is on convenience and efficiency. Convenience sampling is often used in market research, opinion polls, and customer satisfaction surveys.
• Ethnographic Research: Non-probability sampling is commonly used in ethnographic research, which involves studying the social and cultural practices of a particular group or community. Ethnographic research often uses purposive sampling to identify participants who can provide insights into the cultural practices and beliefs of the group being studied.
• Case Studies: Non-probability sampling is often used in case studies, which involve in-depth analysis of a single individual, organization, or event. Case studies often use purposive sampling to select the individual or organization that is most relevant to the study.
• Action Research: Non-probability sampling is also used in action research, which involves developing solutions to practical problems in real-world settings. Action research often uses purposive sampling to identify participants who can provide input and feedback on the proposed solutions.
• Behavioral Research: Non-probability sampling is used in behavioral research where the focus is on understanding human behavior, attitudes, and beliefs. Behavioral research often uses purposive sampling to identify participants who can provide insights into the behavior being studied.
• Historical Research: Non-probability sampling is used in historical research, which involves studying events and phenomena that occurred in the past. Historical research often uses purposive sampling to identify participants who have knowledge or experience relevant to the historical event or phenomenon being studied.

### Purpose of Non-probability Sampling

The main purpose of non-probability sampling is to obtain a sample that is more convenient and practical than a random sample, particularly in situations where a random sample is not feasible, practical, or affordable. Non-probability sampling methods are often used in exploratory research, qualitative research, or in situations where researchers want to study a specific group or population.

### When to use Non-probability Sampling

Here are some situations where non-probability sampling may be appropriate:

• Small or hard-to-reach populations: When the population of interest is small or difficult to access, non-probability sampling may be the only feasible option.
• Exploratory research: Non-probability sampling may be used in exploratory research studies where the objective is to generate hypotheses or insights for further investigation.
• Convenience sampling: This type of non-probability sampling is commonly used when the researcher selects the most convenient participants available, such as those who are nearby or easily accessible.
• Expert or judgmental sampling: When the researcher is interested in studying a specific group of individuals with specialized knowledge or expertise, expert or judgmental sampling may be used.
• Quota sampling: In quota sampling, the researcher identifies relevant characteristics of the population of interest and selects participants based on those characteristics in order to ensure a representative sample.

### Characteristics of Non-probability Sampling

Here are some characteristics of non-probability sampling:

• Non-random selection: In non-probability sampling, the selection of participants is non-random and based on subjective criteria, such as convenience, availability, or judgment.
• Limited generalizability: Since non-probability sampling does not provide a representative sample of the population, the findings obtained from the sample may not be generalizable to the population as a whole.
• Biased sample: Non-probability sampling can result in a biased sample, which means that the sample is not representative of the population, leading to inaccurate or misleading conclusions.
• No sampling frame: Non-probability sampling does not require a sampling frame, which is a list of all the individuals or units in the population, making it easier and cheaper to conduct the sampling process.
• Subjective judgment: Non-probability sampling requires subjective judgment in selecting participants, which can introduce researcher bias and reduce the objectivity of the research findings.
• Less precision: Non-probability sampling generally provides less precision and accuracy compared to probability sampling methods, which may lead to lower statistical power and weaker inferential conclusions.

Advantages of Non-probability Sampling are as follows:

• Easy to conduct: Non-probability sampling is relatively easy to conduct as it does not require a sampling frame or complex statistical calculations.
• Cost-effective: Non-probability sampling is usually less expensive than probability sampling methods as it does not require a large sample size or specialized equipment.
• Convenient: Non-probability sampling can be convenient as it allows researchers to select participants based on their availability or willingness to participate.
• More suitable for exploratory research: Non-probability sampling is more suitable for exploratory research where the focus is on generating new insights or hypotheses rather than making statistical inferences.
• Better for studying rare phenomena: Non-probability sampling can be more effective for studying rare or hard-to-reach populations, such as drug users or people with specific medical conditions, where a probability sample may be difficult to obtain.
• Allows for more diverse samples: Non-probability sampling can allow for a more diverse sample as it does not require strict randomization, allowing for the inclusion of participants who may not have been included in a probability sample.

Disadvantages of Non-probability Sampling are as follows:

• Limited generalizability: Non-probability sampling does not provide a representative sample of the population, so the findings obtained from the sample may not be generalizable to the population as a whole.
• Biased sample: Non-probability sampling can result in a biased sample, which means that the sample is not representative of the population, leading to inaccurate or misleading conclusions.
• Difficulty in estimating sampling error: Non-probability sampling does not allow for the calculation of sampling error, which is the degree to which the sample estimates differ from the true population values.
• Difficult to replicate: Non-probability sampling can be difficult to replicate as the selection of participants is based on subjective criteria, making it challenging to obtain similar results in subsequent studies.
• Limited statistical power: Non-probability sampling generally provides less precision and accuracy compared to probability sampling methods, which may lead to lower statistical power and weaker inferential conclusions.
• Subjective judgment: Non-probability sampling requires subjective judgment in selecting participants, which can introduce researcher bias and reduce the objectivity of the research findings.