Purposive Sampling vs. Theoretical Sampling

Attribute	Purposive Sampling	Theoretical Sampling
Selection process	Non-random, based on specific criteria	Non-random, based on emerging theory
Sample size	Small, focused on specific characteristics	Varies, based on theoretical saturation
Goal	To select participants who can provide rich information	To develop and refine theoretical concepts
Flexibility	Less flexible, predetermined criteria	More flexible, evolving theory guides sampling

Introduction

Purposive sampling and theoretical sampling are two common methods used in qualitative research to select participants for a study. While both methods aim to gather data that is relevant to the research question, they differ in their approach and underlying principles. In this article, we will compare the attributes of purposive sampling and theoretical sampling to understand their strengths and limitations.

Definition

Purposive sampling, also known as judgmental or selective sampling, is a non-probability sampling technique where researchers deliberately choose participants based on specific criteria that are relevant to the research question. This method allows researchers to select participants who can provide valuable insights or information related to the study's objectives. On the other hand, theoretical sampling is a sampling technique commonly used in grounded theory research, where participants are selected based on emerging theoretical concepts and the need to further develop or refine these concepts.

Sampling Strategy

In purposive sampling, researchers use their judgment and expertise to identify and select participants who can best contribute to the study. This method allows researchers to target specific groups or individuals who possess the knowledge or experience needed to address the research question. In contrast, theoretical sampling involves a more iterative and flexible approach, where participants are selected based on the emerging theoretical framework of the study. Researchers continuously collect and analyze data to identify gaps in the theory and select new participants to fill these gaps.

Sample Size

When it comes to sample size, purposive sampling typically involves a smaller number of participants compared to theoretical sampling. Since purposive sampling focuses on selecting participants who can provide rich and in-depth information, researchers often prioritize quality over quantity. On the other hand, theoretical sampling may involve a larger sample size, as researchers aim to gather diverse perspectives and experiences to refine the emerging theory. The sample size in theoretical sampling can vary depending on the complexity of the research question and the depth of the theoretical framework.

Data Collection

In terms of data collection, purposive sampling allows researchers to gather detailed and context-specific information from selected participants. Researchers can use various methods such as interviews, focus groups, or observations to collect data that aligns with the research objectives. Theoretical sampling, on the other hand, involves a more dynamic and iterative process of data collection. Researchers continuously collect and analyze data to test and refine the emerging theory, leading to a deeper understanding of the research phenomenon.

Generalizability

One of the key differences between purposive sampling and theoretical sampling is the issue of generalizability. Purposive sampling is often criticized for its limited generalizability, as the sample is not randomly selected and may not represent the broader population. However, the goal of purposive sampling is not to generalize findings to a larger population but to gain in-depth insights into specific phenomena. Theoretical sampling, on the other hand, aims to develop a theory that can be applied to similar contexts or populations, leading to greater potential for generalizability.

Conclusion

In conclusion, purposive sampling and theoretical sampling are two distinct sampling methods that offer unique advantages and challenges in qualitative research. While purposive sampling allows researchers to select participants based on specific criteria and gather detailed information, theoretical sampling offers a more dynamic and theory-driven approach to data collection. Researchers should carefully consider the research question, objectives, and theoretical framework when choosing between these two sampling methods to ensure the validity and reliability of their findings.