Sampling Techniques
Sampling where every member of the population has a known, non-zero chance of being selected.
Example: Randomly selecting 100 students from a university of 5,000 for a survey.
What is Simple Random Sampling (SRS)?
Every individual in the population has an equal chance of being selected.
Example: Drawing names from a hat.
Advantage: Unbiased and easy to understand.
Disadvantage: Impractical for very large populations.
Example: Drawing 50 names from a hat containing all employee names.
What is Systematic Sampling?
Selecting every k-th individual from a list after a random start.
Advantage: Simple, evenly spread sample.
Disadvantage: Can be biased if there’s a pattern.
Example: Choosing every 10th customer entering a store.
What is Stratified Sampling?
Dividing the population into subgroups (strata) and randomly sampling from each.
Advantage: Ensures subgroup representation.
Disadvantage: Requires knowledge of population characteristics.
Surveying 20% of students from each grade level in a school.
What is Cluster Sampling?
Dividing population into clusters, randomly selecting clusters, and sampling all members of selected clusters.
Advantage: Cost-effective for large populations.
Disadvantage: Higher sampling error than stratified sampling.
example: Selecting 3 schools from a city and surveying all students in those schools.
What is Multistage Sampling?
Combination of sampling methods (e.g., cluster first, then random sampling within clusters).
Advantage: Flexible and practical.
Disadvantage: Complex analysis.
Example: Selecting cities, then neighborhoods within cities, then households within neighborhoods.
What is Non-Probability Sampling?
Sampling where not every member has a known or equal chance of being selected.
Example: Surveying people in a mall because they are easy to reach.
What is Convenience Sampling?
Selecting individuals who are easily accessible.
Advantage: Quick and easy.
Disadvantage: High bias, not representative.
Example: Asking colleagues in your office to complete a questionnaire.
What is Judgmental (Purposive) Sampling?
Selecting individuals based on the researcher’s judgment or expertise.
Advantage: Useful for specialized research.
Disadvantage: Subjective and potentially biased.
Example: Interviewing top scientists to evaluate a new technology.
What is Quota Sampling?
Ensuring the sample reflects certain characteristics of the population, but selection is non-random.
Advantage: Guarantees subgroup representation.
Disadvantage: Selection bias possible.
Example: Surveying 50 men and 50 women at a park, choosing whoever is available.
Difference between Probability & Non-Probability Sampling?
Probability: known chance of selection, unbiased.
Non-Probability: unknown/unequal chance, more bias.
Advantages vs Disadvantages of Probability Sampling
Advantage: statistically valid, less bias.
Disadvantage: can be costly or complex.
Advantages vs Disadvantages of Non-Probability Sampling
Advantage: quick, easy, practical.
Disadvantage: higher risk of bias, less representative.
