TECHNIQUES OF SAMPLING: PROBABILITY SAMPLING AND NON PROBABILITY SAMPLING

0BJECTIVES

1. Understand the purpose and importance of sampling in research.
2. Differentiate between probability and non-probability sampling methods.
3. Identify scenarios where each technique is appropriate.
4. Evaluate the strengths, weaknesses, and biases associated with different sampling techniques.

Techniques of Sampling: Probability and Non-Probability Sampling

Sampling is a fundamental process in research methodology. It allows researchers to make inferences about a population by studying a subset of it. Sampling techniques are broadly categorized into probability sampling and non-probability sampling, each serving distinct research purposes and methodologies.

Probability Sampling Techniques

Probability sampling involves the random selection of samples, ensuring that every individual in the population has an equal chance of being chosen. This method enhances the representativeness of the sample and reduces bias.

 1.Simple Random Sampling

In simple random sampling, every individual in the population is assigned a unique identifier, and samples are selected using random mechanisms such as lottery or random number generators.

Example: Selecting 50 students randomly from a university enrolment list.

2.Systematic Sampling

In this method, samples are selected at regular intervals from an ordered population. For instance, selecting every 10th individual from a list of 1,000 people.

3.Stratified Sampling

The population is divided into homogeneous subgroups (strata), and samples are taken from each stratum proportionally. This technique is useful when the population has distinct subcategories.

Example: Dividing a population by income levels and sampling within each group.

4.Cluster Sampling

Instead of sampling individuals, entire clusters or groups are randomly selected. For example, choosing schools randomly and then surveying all students within selected schools.

Non-Probability Sampling Techniques

Non-probability sampling does not involve random selection, and the samples are chosen based on the researcher’s judgment or convenience. While this approach may introduce bias, it is often practical and cost-effective.

Convenience Sampling

Samples are chosen based on availability and ease of access. For example, surveying people at a mall.

Purposive Sampling

  Researchers select participants based on specific characteristics or criteria   relevant to the study. For example, selecting only experienced teachers for a study on teaching methods.

 

Quota Sampling

A specific quota is set for different subgroups, and samples are chosen until the quota is met. For instance, surveying 50 men and 50 women for gender-based analysis.

Snowball Sampling

Participants recruit others from their network, making it useful for studying hard-to-reach populations.

Example: Researching social behaviors among underground artists.

Table 1

Comparing Probability and Non-Probability Sampling

Aspect	Probability Sampling	Non-Probability Sampling
Basis of Selection	Random selection	Non-random selection
Bias	Minimizes bias	May involve bias
Representativeness	High	Variable
Cost and Time	Often expensive and time-consuming	Cost-effective and quicker
Applicability	Suitable for large-scale quantitative research	Common in qualitative and exploratory research

 

Conclusion

The choice of sampling technique depends on the research objectives, resources, and the nature of the population under study. Probability sampling is preferred for generalizing results, while non-probability sampling is suitable for exploratory or specialized research contexts.

 References

Babbie, E. R. (2020). The Practice of Social Research. Cengage Learning.

Bryman, A. (2016). Social Research Methods. Oxford University Press.

Creswell, J. W. (2014). Research Design: Qualitative, Quantitative, and Mixed Methods Approaches. SAGE Publications.

Flick, U. (2018). An Introduction to Qualitative Research. SAGE Publications.

Kothari, C. R. (2004). Research Methodology: Methods and Techniques. New Age International.

Neuman, W. L. (2014). Social Research Methods: Qualitative and Quantitative Approaches. Pearson.

Patton, M. Q. (2015). Qualitative Research & Evaluation Methods. SAGE Publications.

Teddlie, C., & Tashakkori, A. (2009). Foundations of Mixed Methods Research. SAGE Publications.

Yin, R. K. (2018). Case Study Research and Applications: Design and Methods. SAGE Publications.

Zikmund, W. G. (2003). Business Research Methods. South-Western.

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