MULTISTAGE

RANDOM

SAMPLINGDR. RITESH SHIWAKOTI

MScD PROSTHODONTICS

S NO: 20130204556

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.

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.

Multistage sampling refers to sampling

plans where the sampling is carried out in

stages.

Using smaller and smaller unit at each stage

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

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.

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.

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 .

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.

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

Disadvantages

Not as accurate as Simple Random

Sample if the sample is the same size

More testing is difficult to do