If it is not essential to conduct a complete enumeration, then a sample of some suitable size is selected from the population and the study is carried out on the sample. This study is called a sample survey. Most research work is done through sample surveys. The opinion of the voters in favor of certain proposed election candidates is obtained through sample surveys.
Advantages of Sampling
Sampling has some advantages over doing a complete count.
- Need for Sampling
Sometimes there is a need for sampling. Suppose we want to inspect eggs, bullets, missiles or tires produced by 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 or the bullets, etc. We have to take care that the wastage is minimal. This is possible only in a 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 compared to the population, the time and cost involved in sample study are much less than complete counts. For complete counts huge funds are required, and there is always the problem of finances. A small sample can be studied in a limited amount of time and the total cost of a sample study is very small. For a complete count, we need a big team of supervisors and enumerators who must be trained and paid properly for the work they do. Thus, a sample study requires less time and less cost.
If we collect information about all the units of a population, the collected information may be true, however 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 the information, so we say that 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 experiments are done on a sample basis. For example, fertilizers, seeds and medicines are initially tested on samples and if they are found to be effective, then they are applied on large scale. Most of the research work is done on samples.
Sample data is also used to check the accuracy of census data.