If it is not essential to conduct the complete enumeration, then a sample of some suitable size is selected form the population and the study is carried out on the sample. This study is called sample survey. Most of the research work is done through sample surveys. The opinion of the voters in favor of certain proposed election candidates is obtained through sample survey.
Advantages of Sampling:
Sampling has some advantages over the complete count. These are:
- Need for Sampling:
Sometimes there is a need for sampling. Suppose we want to inspect the eggs, the bullets, the missiles and the tires of some firm. The study may be such that the objects are destroyed during the process of inspection. Obviously, we cannot afford to destroy all the eggs and the bullets etc. We have to take care that the wastage should be minimum. This is possible only in sample study. Thus sampling is essential when the units under study are destroyed.
- Saves Time and Cost:
As the size of the sample is small as compared to the population, the time and cost involved on sample study are much less than the complete counts. For complete count huge funds are required. There is always the problem of finances. A small sample can be studied in a limited time and total cost of sample study is very small. For complete count, we need a big team of supervisors and enumeration who are to be trained and they are to be paid properly for the work they do. Thus the sample study requires less time and less cost.
If we collect the information about all the units of population, the collected information may be true. But we are never sure about it. We do not know whether the information is true or is completely false. Thus we cannot say anything with confidence about the quality of information. We say that the reliability is not possible. This is a very important advantage of sampling. The inference about the population parameters is possible only when the sample data is collected from the selected sample.
Sometimes the experiments are done on sample basis. The fertilizers, the seeds and the medicines are initially tested on samples and if found useful, then they are applied on large scale. Most of the research work is done on the samples.
Sample data is also used to check the accuracy of the census data.