In sampling methods, what does it mean to sample without replacement?

• A. Each unit in the population has an equal probability of being selected on every draw, even if it was selected before.
• B. Units are selected by dividing the population into strata and sampling from each stratum.
• C. Once a unit is selected from the population, it cannot be selected again in the same sample.
• D. The population is so large relative to the sample that draws can be treated as independent.

Answer: (C)

Verified step by step guidance

1. Understand that sampling without replacement means that once a unit (or individual) is selected from the population, it is removed from the pool and cannot be chosen again in the same sample.
2. Recognize that this contrasts with sampling with replacement, where each unit can be selected multiple times because it is 'replaced' back into the population after selection.
3. Note that in sampling without replacement, the probabilities of selecting subsequent units change after each draw because the population size decreases by one each time a unit is selected.
4. This method ensures that all units in the sample are unique, which can affect the calculation of probabilities and variances in statistical analysis.
5. Remember that sampling without replacement is often used when the population is finite and the sample size is a significant fraction of the population.