**Question:** A region is divided into 50 villages for the purpose of a survey. 10 villages are then selected randomly for the purpose of a study. This type of sampling is termed as -

A. Simple Random Sampling
B. Stratified Sampling
C. Systematic Sampling
D. Cluster Sampling

**Correct Answer:** D. Cluster Sampling

**Core Concept:** Sampling is a statistical method used to select a sample of subjects or units from a larger population for the purpose of research or survey. Different sampling techniques are used for different scenarios, depending on the characteristics and size of the population.

**Why the Correct Answer is Right:** Cluster sampling is a type of probability sampling technique where a larger population is divided into smaller groups (clusters) and then samples are drawn from these clusters. In this case, the 50 villages act as clusters. By selecting villages randomly from these clusters (in this case, the villages), a representative sample can be obtained from the larger population (the region).

**Why Each Wrong Option is Incorrect:**

A. Simple Random Sampling: In simple random sampling, every unit in the population has an equal chance of being selected, which is not the case here as villages are already divided into clusters (the villages).

B. Stratified Sampling: Stratified sampling involves dividing the population into subgroups, and then selecting samples from each subgroup randomly. In this question, the villages are already divided into clusters (the villages), so stratified sampling is not applicable.

C. Systematic Sampling: In systematic sampling, every nth individual, item, or unit is chosen from the population. This method is not suitable when the sampling units (villages) are already grouped into clusters (the villages).

**Clinical Pearl:** Cluster sampling is useful when the population is large and geographically dispersed, making it impractical to select individuals directly from the population. It is commonly used in public health surveys and epidemiological studies.

**Example:** Suppose we want to study the prevalence of diabetes in the region. We can divide the region into clusters (the 50 villages) and then randomly select villages (the clusters) for further examination. By doing so, we can obtain a representative sample of the larger population (the region) while avoiding the practical challenges of directly sampling individuals.