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What is What kind of sampling should be done when there is a small group of patients, easily available? and explain in detail?
Random sampling (simple random sampling)
- It is a technique whereby each sampling unit has the same probability of being selected. 
- Random sampling is done, when there is a small group of patients. 
Multiphase sampling: 
- This is used to take basic data from a large sample and details from a sub-sample.
Multistage sampling
- The first stage is to select the groups or clusters. Then, subsamples are taken in as many subsequent stages as necessary to obtain the desired sample size. 
Eg: 
1st stage: Choice of states within countries. 
2nd stage: Choice of towns within each state.
3rd stage: Choice of neighborhoods within each town.
Soben Peter 
Essentials of preventive and community dentistry 
4th edition