Learning Objectives

  • Identify the circumstances that make sampling unnecessary and the reason they are rare.
  • Identify the relation between the desired sample, the obtained sample, the sampling frame, and sample quality.
  • Define and distinguish probability and nonprobability sampling.
  • Define the major types of probability sampling method and indicate when each is preferred.
  • Explain when nonprobability sampling methods may be preferred.
  • Describe the concept of sampling error and explain how its size is affected by the number of cases sampled, the heterogeneity of the population, and the fraction of population included in the sample.