Ryvässatunnaisvalinta

Ryvässatunnaisvalinta, meaning "cluster random sampling" in English, is a statistical sampling method where the entire population is divided into groups called clusters. Instead of selecting individual elements from the population, a sample of clusters is randomly chosen. Once the clusters are selected, all individuals within those chosen clusters are included in the sample. This method is often used when it's impractical or too costly to survey every individual in a large, geographically dispersed population.

The primary advantage of cluster sampling is its efficiency and cost-effectiveness. It can significantly reduce the time and resources required for data collection compared to simple random sampling, especially when the population is spread out. For example, if a researcher wants to study school children in a country, they might divide the country into districts (clusters) and then randomly select a few districts to survey. All schools within the chosen districts would then be surveyed.

However, cluster sampling can introduce sampling bias if the clusters are not representative of the entire population. The variability within clusters might be smaller than the variability between clusters, which can affect the precision of the estimates. To mitigate this, researchers often use multi-stage cluster sampling, where clusters are further subdivided into smaller sub-clusters, and then a random sample of sub-clusters is selected. This approach can improve the representativeness of the sample.