Quota sampling

Quota sampling is a non-probability sampling technique wherein the researcher ensures equal representation of subsets of a population by selecting a specific number of observations from each subset. This method is used when the researcher wants to study specific sub-groups within a population but does not require the random selection necessary for probability sampling methods like simple random sampling or stratified sampling.

Overview

Quota sampling involves the division of a population into exclusive sub-groups, known as strata. The researcher then determines the proportion of each stratum to be sampled, based on pre-set quotas reflective of the stratum's proportion in the population. This approach allows for the targeted study of specific groups, ensuring that the sample reflects the diversity within the population.

Procedure

The process of quota sampling can be broken down into several steps:

1. Identification of Strata: The population is divided into strata based on characteristics relevant to the research study, such as age, gender, income level, etc.
2. Determination of Quotas: For each stratum, the researcher decides the number of subjects to be included in the sample, based on the stratum's representation in the population.
3. Selection of Subjects: Subjects are selected based on the predefined quotas. The selection within each stratum is non-random, often relying on convenience or judgmental sampling.

Advantages

Quota sampling offers several advantages:

• Cost-Effectiveness: It is less costly and time-consuming than probability sampling methods.
• Simplicity: The method is straightforward and easy to understand, making it accessible for researchers with limited resources.
• Flexibility: Researchers can easily adjust quotas to ensure representation of key sub-groups.

Disadvantages

However, quota sampling also has its drawbacks:

• Bias: The non-random selection of subjects can introduce bias, affecting the generalizability of the results.
• Lack of Representativeness: Without random selection, the sample may not accurately represent the population.
• Difficulty in Determining Sample Size: Determining the appropriate quotas for each stratum can be challenging, especially in diverse populations.

Applications

Quota sampling is widely used in market research, opinion polling, and preliminary research where the goal is to get a quick, representative snapshot of the population rather than to generalize findings to the entire population.

Comparison with Other Sampling Methods

Quota sampling is often compared to stratified sampling, a probability sampling method. While both involve dividing the population into strata, stratified sampling requires random selection within each stratum, which helps to minimize selection bias and improve the representativeness of the sample.

Conclusion

Quota sampling is a valuable tool for researchers seeking to understand specific sub-groups within a population. While it offers several practical advantages, its non-random selection process can introduce bias, making it less suitable for studies requiring high levels of generalizability.