2. Multistage sampling is a complex form
of cluster sampling.
we use variety of sampling methods
together.
Sampling scheme that combine several
methods are called multistage samples.
3. Most survey conducted by professional
polling organization use some
combination of stratified and cluster
sampling as well as simple random
sampling.
Thus forming a multi stage random
sampling.
4. Multistage sampling refers to sampling
plans where the sampling is carried out in
stages.
Using smaller and smaller unit at each stage
5. In this method, the whole population is
divided in first stage sampling unit from
which random sample are selected.
The selected first stage is then subdivided
into second stage units from which
another sample is selected.
Third and fourth stage sampling is done in
same manner if necessary
6. Multistage designs are used in many
practical cases.
These are just a few :Large surveys
involving the sampling of housing units -
The U.S. Census Bureau selects
geographical areas within each state and
then select housing units within each
selected geographical area.
7. Practical quality control problems often
involve two (or more) stages of sampling.
For example, Ford wants to inspect the
quality of a supplier of air filters. They first
sample some cartons and then inspect
some air filters inside these selected
cartons.
Gallop poll samples approximately 300
election districts. At the second stage,
they select 5 households per district.
8. NFHS ( national family health survey) data
is collected by multistage sampling.
Rural areas2 stage sampling village
form list by PPS( probability proportional to
size), household from the village .
9. For example, household surveys conducted
by the Australian Bureau of Statistics begin by
dividing metropolitan regions into 'collection
districts' and selecting some of these
collection districts (first stage).
The selected collection districts are then
divided into blocks, and blocks are chosen
from within each selected collection district
(second stage).
Next, dwellings are listed within each selected
block, and some of these dwellings are
selected (third stage). This method makes it
unnecessary to create a list of every dwelling
in the region and necessary only for selected
blocks.
10. Advantages
Cost and speed that the survey can be
done in less.
Convenience of finding the survey sample
Normally more accurate than cluster
sampling for the same size sample
11. Disadvantages
Not as accurate as Simple Random
Sample if the sample is the same size
More testing is difficult to do
