Sampling Techniques to Know for AP Research

Sampling techniques are essential for gathering data in research. They help ensure that results are accurate and representative, which is crucial in fields like biostatistics, political research, and data science. Understanding these methods enhances decision-making and inference.

1. Simple Random Sampling

   • Every member of the population has an equal chance of being selected.
   • Selection is typically done using random number generators or drawing lots.
   • Reduces bias and allows for generalization of results to the entire population.

2. Stratified Sampling

   • The population is divided into distinct subgroups (strata) based on specific characteristics.
   • Samples are drawn from each stratum to ensure representation.
   • Increases precision and reduces variability in estimates.

3. Cluster Sampling

   • The population is divided into clusters, often geographically, and entire clusters are randomly selected.
   • Useful when populations are large and spread out.
   • Reduces costs and time but may introduce higher variability if clusters are not homogeneous.

4. Systematic Sampling

   • A starting point is randomly selected, and then every nth member is chosen from the list.
   • Simple to implement and ensures even coverage of the population.
   • Can introduce bias if there is a hidden pattern in the population list.

5. Convenience Sampling

   • Samples are taken from a group that is easily accessible.
   • Quick and cost-effective but often leads to biased results.
   • Not representative of the entire population, limiting generalizability.

6. Quota Sampling

   • Researchers ensure equal representation of specific characteristics by setting quotas.
   • Participants are selected non-randomly until quotas are met.
   • Can lead to bias as it does not involve random selection.

7. Purposive Sampling

   • Participants are selected based on specific characteristics or criteria relevant to the study.
   • Useful for qualitative research where specific insights are needed.
   • Results may not be generalizable to the broader population.

8. Multistage Sampling

   • Combines multiple sampling methods, often starting with cluster sampling followed by random sampling within clusters.
   • Useful for large and complex populations.
   • Increases efficiency while maintaining representativeness.

9. Probability Sampling

   • All members of the population have a known chance of being selected.
   • Includes methods like simple random, stratified, and cluster sampling.
   • Allows for statistical inference and generalization of results.

10. Non-Probability Sampling

    • Not all members have a chance of being selected; selection is based on non-random criteria.
    • Includes methods like convenience, quota, and purposive sampling.
    • Results may be biased and not suitable for statistical inference.

11. Snowball Sampling

    • Existing study subjects recruit future subjects from their acquaintances.
    • Useful for hard-to-reach populations or when a sampling frame is not available.
    • Can lead to bias as it relies on social networks.

12. Voluntary Response Sampling

    • Participants self-select to be part of the study, often through surveys or polls.
    • Easy to implement but highly susceptible to bias.
    • Results may reflect the opinions of those with strong feelings about the topic.

13. Random Digit Dialing

    • A method used primarily in telephone surveys where random phone numbers are generated.
    • Ensures a random selection of participants from a population.
    • Can be limited by non-response rates and the prevalence of mobile phones.

14. Proportional Sampling

    • Samples are drawn in proportion to the size of each subgroup within the population.
    • Ensures that each subgroup is represented according to its size.
    • Enhances the accuracy of estimates for each subgroup.

15. Disproportional Sampling

    • Samples are drawn in unequal proportions from different subgroups.
    • Useful when certain subgroups are of particular interest.
    • May require weighting in analysis to ensure accurate representation.