Cluster Sampling
Definition
A design in which the population is divided into naturally occurring groups called clusters, a random sample of clusters is selected, and all or a random subset of units within each selected cluster are examined. Used when a complete sampling frame of individuals is unavailable.
- Design type
- Probability sampling by group
- Unit selected
- Naturally occurring clusters
- Use case
- No complete sampling frame of individuals
- Within cluster
- All or a random subset examined
Common questions
Why would an investigator use cluster sampling instead of simple random sampling?+
Simple random sampling requires a full list of every individual unit, which is often unavailable or impractical to build, such as every pill in a large seized batch; cluster sampling instead selects whole groups, like boxes or bags, that already exist as a natural grouping, then samples within them.
What is the tradeoff of using cluster sampling for forensic evidence quantities?+
It is more practical when a complete frame does not exist, but it typically has higher sampling variance than simple random sampling because units within the same cluster tend to be more similar to each other than to units in other clusters, which can affect confidence in the resulting estimate.
Related terms
- Sampling Bias
- A systematic distortion in an estimate caused by a selection process that does not give all units a known probability of inclusion....
- Sampling Error
- The difference between a sample statistic and the true population value, arising from the randomness of selection. It can be estimated from...
- Sampling Frame
- The list or description of all units from which the sample can be drawn. Any unit not on the frame cannot be...
- Simple Random Sampling
- A design in which every possible subset of a given size has an equal probability of being selected. It requires a complete...
- Stratified Sampling
- A sampling design that divides the population into homogeneous subgroups (strata) and samples each stratum separately. Allows the auditor to apply higher...