# Learning Objectives

1. Distinguish the two foci of sampling theory.

2. Identify the circumstances that make sampling unnecessary and the reason they’re rare.

3. Identify the relation between the elements, the sampling units, the sample, the sampling frame, and the target population.

4. Define the concept of representative sample, and explain how it contrasts with the concept of bias.

5. Define and distinguish probability and nonprobability sampling.

6. Define the major types of probability sampling methods, and indicate when each is preferred.

7. Explain when nonprobability sampling methods may be preferred.