All items in any field of inquiry constitute a ‘ Universe ’ or ‘ Population.’ A complete enumeration of all items in the population is known as a census inquiry. It can be presumed that in such an enquiry, when all items are covered, no element of chance is left and highest accuracy is obtained. But in practice this may not be true. Even the slightest element of bias in such an inquiry will get larger and larger as the number of observation increases. Moreover, there is no way of checking the element of bias or its extent except through a resurvey or use of sample checks. Besides, this type of inquiry involves a great deal of time, money and energy. Therefore, when the field of inquiry is large, this method becomes difficult to adopt because of the resources involved. At times, this method is practically beyond the reach of ordinary researchers. Perhaps, government is the only institution which can get the complete enumeration carried out. Even the government adopts this in a very rare cases such as population census conducted once in a decade. Further, many a time it is not possible to examine every item in the population, and sometimes it is possible to obtain sufficiently accurate results by studying only a part of total population. In such cases there is no utility of census surveys. A census refers to a count or a study of all of the elements in the ‘ Population’. As is quite obvious it is generally more economical in time, efforts and money to get the desired information for only some of the elements ( sample ) than for all of them, i.e., the population. When we select some of the elements ( sample ) with the intention of finding out something about the population from which they are taken, we refer to that sub - group of elements of a ‘ Sample ’. Our expectation, in studying the sample, is of course, that what we find out from the sample, will be true of the ‘ population ’ as a whole. Actually this may not
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