CEVAP:

When we try to obtain some information about the characteristics of a population there are important reasons why we use a sample instead of a census. The main reasons for sampling can be categorised by the following topics:

Cost: Every project has a limited funding. The investigator uses the funding wisely. A sampling often provides reliable and useful information at much lower cost than does a census.

Time: A sampling survey often provides more timely information than a census, because fewer data have to be collected and analysed. Thus, the required information can be achieved quickly.

Accuracy: While a census data is gathered, many unexpected problems may affect the accuracy of the results such as recording errors, copying errors, false recordings by interviewers etc. So, while working with census data, we may inadvertently come across with a figure for a population parameter being further away than the actual value. With a good sampling procedure using good sampling methods and by choosing random observations, actually we can be very close to the true value of the population parameter. Since usually the size of the sample is not very big, data errors are more controllable.

Physical Impossibility: Some populations are uncountable or infinite to conduct a census. In this situation, it is impossible to consider all the elements of a population. Thus, a sample is necessary to obtain information from a population.

Destructive Tests: If a test includes the destruction of an item or product, sampling should be used.