Concept of Sampling

In the modern world, facts and figures are sine-qua-non for balanced development, transparent governance and efficient administration. In order to achieve the above, carefully worked out plans are drawn up and executed as far as possible. To formulate these in a scientific manner, it is essential to have basic facts in numerical terms for various groups, regions in the century and for the country as a whole.
It is beyond the resources of countries and more often impossible to collect facts on regular basis from each person, establishment or farm in the country. Fortunately, as we know it is not required to enumerate each unit in the population to arrive at an acceptable figure, known as estimate of the of the population parameter. A well-designed sample can be providing an accurate estimate that a country needs at a cost the country may well afford.

During the past 30 years or so, the methods and techniques of sampling have reached a high level of scientific development. As a result, the uses of sampling have been extended into a wide variety of fields. From the standpoint of statistical data collection, sampling is a means for selecting a relatively small of households, persons or others units for inclusion in a survey of some kind and inferring conclusions based on these limited number for instances. This selection is done because enumeration of all units in the target population (population for which information is needed) is a large and complex undertaking that is usually affected by limitations of time, budget and availability of experienced personnel. Not only that, it is unnecessary as well as from the standpoint of precision and statistical reliability. Many countries have found, moreover, that sampling can play an important role in an overall census program.
Let us now introduce the concept of sampling by an example.
Example 01: Very frequently, we talk about banning or restricting student’s politics in the university campus. This is a very sensitive issue. We sometimes wonder whether our views on this issue are shared by the student community, who are directly or indirectly involved in this important issue. We may want to know the actual percentage of students of Dhaka University who do not approve of banning students politics in the campus. This percentage could be obtained by asking every student in the campus if he/she approves or disapproves of this. The procedure, however, would be quite time-consuming, expensive and probably impracticable. To overcome this, we might choose only a small portion of the students and try to infer the attitude of all the students based on the answers received from this portion of students.
This is a typical example of statistical inference. The procedure of choosing the portion of students from the entire student body is technically known as sampling. The portion of the students referred to above is called sample and the entire student body a population.

Definition: Sampling is a scientific process of selecting a part from a statistical population and may embrace the derivation of estimates and any inferences derived from them for that population.