Stratified Sampling

Definition

Stratified sampling is a technique used in statistics where the population is divided into distinct subgroups, or strata, that share similar characteristics, and samples are drawn from each of these groups. This method ensures that the sample reflects the diversity within the population, enhancing the representativeness and accuracy of survey results.

5 Must Know Facts For Your Next Test

1. Stratified sampling can lead to more precise estimates compared to simple random sampling, especially when there are significant differences among strata.
2. The allocation of sample sizes to different strata can be proportional or optimal, depending on research goals and resource constraints.
3. Stratified sampling helps in reducing sampling error by ensuring representation from all relevant subgroups within the population.
4. This technique is particularly useful in studies involving diverse populations, such as health surveys where various demographic factors impact health outcomes.
5. The effectiveness of stratified sampling depends on correctly identifying and defining the strata before sampling begins.

Review Questions

• How does stratified sampling improve the representativeness of survey results compared to other sampling methods?
  • Stratified sampling improves representativeness by ensuring that all relevant subgroups of the population are included in the sample. By dividing the population into strata based on shared characteristics and then randomly selecting samples from each stratum, researchers can capture the diversity within the population. This approach reduces bias and increases the likelihood that survey findings accurately reflect the entire population's opinions or behaviors.
• Discuss the factors that determine how sample sizes are allocated to different strata in stratified sampling.
  • Sample size allocation to different strata can be determined by several factors, including the relative size of each stratum in the population, the variability of responses within each stratum, and research objectives. For example, if one stratum is much larger than others but shows greater variability in responses, a proportional allocation may be beneficial. Alternatively, researchers might choose optimal allocation methods to ensure precision while managing resource limitations effectively.
• Evaluate the impact of incorrectly defined strata on the outcomes of stratified sampling studies.
  • Incorrectly defining strata can lead to significant issues in stratified sampling studies, as it may result in misrepresentation of certain groups or even biases in data collection. If strata do not accurately reflect meaningful characteristics related to the research question, the insights derived from the study may not be valid. Consequently, this could skew results and ultimately misinform decision-making based on those findings, highlighting the importance of careful stratum identification during study design.

Related terms

Strata:

Strata are the distinct subgroups within a population that are identified in stratified sampling, each representing a specific characteristic such as age, income, or education level.

Sample Size: Sample size refers to the number of observations or replicates included in a sample, which can significantly influence the precision and reliability of survey results.

Random Sampling:

Random sampling is a method where each member of the population has an equal chance of being selected, often used in conjunction with stratified sampling to ensure that samples within strata are unbiased.