Multistage Sampling Method

In two-stage cluster sampling, a simple random sample of clusters is selected and then a simple random sample is selected from the units in each sampled cluster.

Multi stage sampling is a generalisation of two stage sampling. As the name suggests, multi stage sampling is carried out in different stages. In each stage progressively smaller (population) geographic areas will be randomly selected. 

Example:

A political pollster interested in assembly elections in Andhra Pradesh may first divide the state into different assembly units and a sample of assembly constituencies may be selected in the first stage.

In the second stage, each of the sampled assembly constituents are divided into a number of segments and a second stage sampled assembly segments may be selected.

In the third stage within each sampled assembly segment either all the house-holds or a sample random of households would be interviewed.

In this sampling method, it is possible to take as many stages as are necessary to achieve a representative
sample. Each stage results in a reduction of sample size.

In a multi stage sampling at each stage of sampling a suitable method of sampling is used. More number of stages are used to arrive at a sample of desired sampling units.

Advantages

a) Multistage sampling provides cost gains by reducing the data collection on costs.

b) Multistage sampling is more flexible and allows us to use different sampling procedures in different stages of sampling.

c) If the population is spread over a very wide geographical area, multistage sampling is the only sampling method available in a number of practical situations.

Limitations

a) If the sampling units selected at different stages are not representative multistage sampling becomes less precise and efficient.