A survey can be conducted by personal interviews, by telephone, by mail or by email. The personal interview technique has the advantage of having a high response rate and a high quality of answers obtained. However, it is the most expensive technique. A survey conducted by mail or email is the least expensive method but the response rate is usually very low.
Sample surveys can be used in
market researching
quality controls
opinion polls
society researching
There is always an uncertainty of the results, because of the sample. The reliability can be increased by a larger sample an also by using better measuring instruments.
A simple random sample
A simple random sample is a sample that is selected in such a way that each member of the population has the same chance of being included in the sample.