The word "sample" is well known in everyday life and it is fairly understood in the sense that it is a part of a large bulk which represents the whole bulk and the characteristics possessed by this part are the same as that of the bulk. It is common experience that in a grape market the customer takes a handful of warb out of the lot to find out the quality of that lot. This process of selecting a part out of the lot which serves as a representative of the whole lot is known as sampling. The part which is taken out of the bulk is called the "sample", and the whole bulk is called "universe" or "population". Sampling procedure demands sub-division of the material to be sampled into units. These units, on the basis of which sampling procedure is based is technically known as sampling units. These sampling units may be of natural or artificial units. Individuals or human being are natural units while individuals distributed according to their income are artificial units or unnatural units. It is obvious that greater the size of the sample, the smaller the sampling error. A good sample or an unbiased sample is known as random sample.
