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-
First, I remember different types of sampling methods. Cluster sampling involves dividing the population into groups (clusters) and randomly selecting entire clusters. In this case, the villages are the clusters. So if they randomly pick 10 villages out of 50, that's cluster sampling.
Another possibility is stratified sampling, where the population is divided into strata and samples are taken from each. But here, they're selecting entire villages, not specific subgroups within each village. So stratified is less likely.
Simple random sampling would mean selecting individual villages without grouping, but the question mentions dividing into villages first. Systematic sampling involves selecting every nth item, which doesn't fit here either.
So the correct answer should be cluster sampling. The key here is that the entire cluster (village) is the unit of selection. The other options don't fit the description of selecting entire groups. The clinical pearl is to remember that cluster sampling is used when the population is naturally divided into groups, and selecting entire groups is more efficient.
**Core Concept**
This question tests understanding of **sampling methods in epidemiological surveys**. Specifically, it evaluates recognition of **cluster sampling**, where the population is divided into groups (clusters), and entire clusters are randomly selected for study rather than individual units.
**Why the Correct Answer is Right**
In **cluster sampling**, the population is partitioned into distinct groups (e.g., villages), and a random sample of clusters is selected. All members within the chosen clusters are included in the study. This method is logistically efficient for large, geographically dispersed populations, as it reduces costs and simplifies data collection by focusing on predefined clusters (e.g., 10 villages out of 50). It differs from stratified sampling, where subgroups are sampled proportionally, and from simple random sampling, where individual units are selected regardless of grouping.
**Why Each Wrong Option is Incorrect**
**Option A:** *Simple random sampling* involves selecting individual units (e.g., households) randomly, not entire clusters.
**Option B:** *Stratified sampling* divides the population into strata (e.g., age groups) and samples from each stratum, ensuring representation across subgroups.
**Option C:** *Systematic sampling* selects units at regular intervals (e.g., every 5th village), not random cluster selection.
**Clinical Pearl / High-Yield Fact**
Cluster sampling is ideal for **large-scale public health surveys** (e.g., nutritional status in rural areas) where listing all individuals is impractical. Remember: **"Cluster = group as unit"**, whereas **"Strata = subgroup representation"**.
**Correct Answer: D. Cluster sampling**