A cluster sample randomly selects clusters of the population and samples the entire cluster.
For this example, a cluster is one column of the grid.
Two clusters are chosen at random.
There is nothing special about using columns as clusters.
In practice, you would use something like blocks in a city or classrooms in a school as clusters.
The sample size is n=16. This choice was arbitrary to make some of the other examples easier.
It is possible to pick the same cluster more than once.
If you click "Resample" several times, you will see the proportions change.
This is sampling error and is part of the sampling process.
We will spend time later talking about how to deal with sampling error.