Four methods of sampling
Random samples
Random samples are selected by using chance methods or random numbers.
Systematic samples
Systematic samples are obtained by numbering each value in the population and then selecting every value.
Stratified samples
Stratified samples are selected by dividing the population into groups (strata) according to some characteristic and then taking samples from each group.
Cluster samples
Cluster samples are selected by dividing the population into groups and then taking samples of the groups.