All are true about cluster sampling except?
First, I need to recall what cluster sampling is. From my stats class, cluster sampling is when the population is divided into groups (clusters), and a random sample of these clusters is selected. Then, all individuals within the chosen clusters are included in the study. This is different from stratified sampling, where each stratum is sampled proportionally. So the core concept here is the definition and method of cluster sampling compared to other sampling techniques.
Now, the correct answer is the one that's not true. Let's think about the options. The user didn't provide the options, but common distractors in such questions might include confusing cluster sampling with stratified sampling. For example, a wrong option might say that cluster sampling ensures each cluster is representative of the population. Wait, no—cluster sampling actually selects entire clusters, which might not be as representative as stratified sampling. In stratified sampling, each stratum is sampled, ensuring representation. So if an option claims that clusters are homogeneous, that's incorrect because clusters are supposed to be heterogeneous to represent the population as a whole. Wait, actually, clusters are usually heterogeneous because they're natural groupings (like schools or cities), whereas strata are homogeneous. So if an option says clusters are homogeneous, that's wrong.
Another common mistake is thinking that cluster sampling reduces sampling error. Actually, cluster sampling often increases sampling error because individuals within a cluster are more similar to each other than to those in other clusters. So if an option states that cluster sampling decreases variance, that's incorrect. The correct answer would be the one that says cluster sampling increases variance or something like that.
The clinical pearl here is to remember the difference between cluster and stratified sampling. Cluster uses natural groups, selects entire clusters, and can have higher variance. Stratified divides the population into strata and samples from each, leading to more precise estimates. So the key is that cluster sampling is about selecting groups, not individuals, and that clusters are heterogeneous, not homogeneous.
Putting this together, the false statement would be something like "Clusters are homogeneous" or "Cluster sampling is more precise than simple random sampling." The correct answer would be the one that incorrectly describes cluster sampling's characteristics.
**Core Concept**
Cluster sampling divides a population into **clusters** (natural groups), randomly selects entire clusters, and includes all members within those clusters. It is distinct from **stratified sampling**, where strata are sampled proportionally and internally homogeneous. Cluster sampling is cost-effective but often less precise due to intra-cluster homogeneity.
**Why the Correct Answer is Right**
Cluster sampling reduces logistical costs by sampling **entire groups** (e.g., schools, neighborhoods) rather than individuals. Clusters are typically **heterogeneous** (e.g., a school contains diverse students), and the method assumes clusters mirror the population. This increases sampling error compared to stratified sampling, where strata are homogeneous and sampled proportionally.
**Why Each Wrong Option is Incorrect**
**Option A:** “Clusters are homogeneous” – Incorrect. Clusters are **heterogeneous** by design to reflect population diversity.
**Option B:** “Reduces sampling error” – Incorrect. Cluster