Due to the fact that they all contain
elements of random selection, techniques like cluster sampling and
multistage sampling are just as externally valid as simple random sampling due to the fact that they
all contain elements of random selection.
Cluster sampling are more or less
alike, each heterogeneous and resembling the overall population. The population
is split into representative clusters, then a selection is done one or few
from the clusters, then lastly, a census is performed with those selected
clusters.
In multistage sampling, several methods
are combined in sampling schemes and occasionally utilized the same method or different
methods or more than once. Though they have
different steps in being done, they both have random selection elements.
