Before giving the notion of sampling we will first define population. In a statistical investigation the interest usually lies in the assessment of the general magnitude and the study of variation with respect to one or more characteristics relating to individuals belonging to a group. This group of individuals under study is called population or universe, thus in statistics, population is an aggregate of objects, animate or inanimate, under study. The population may be finite or infinite.
It is obvious that for any statistical investigation complete enumeration of the population is rather impracticable. For example, if we want to have an idea of the average per capita income of the people India, we will have to enumerate all the earning individuals in the country, which is rather a very difficult task.
If the population is infinite, complete enumeration is not possible. Also if the units are destroyed in the course of inspection 100% inspection, through possible, is not at all desirable. But even if the population is finite or the inspection is not destructive, 100% inspection is not taken recourse to because of multiplicity of causes, viz, administrative and financial implications, time factor, etc., and we take the help of sampling.
A finite subset of statistical individuals in a population is called a sample and the number of individuals in a sample is called the sample size.
For the purpose of determining population characteristics, instead of enumerating the entire population, the individuals in the sample only are observed. Then the sample characteristics are utilized to approximately determine or estimate the population. For example, on examining the sample of a particular stuff we arrive at a decision of purchasing or rejecting that stuff. The error involved in such approximation is known as sampling error and is inherent and unavoidable in any and every sampling scheme. But sampling results in considerable gains, especially in time and cost not only in respect of making observations of characteristics but also in the subsequent handling of the data.
Sampling is quite often used in our day – to – day practical life. For example, in a shop we assess the quality of sugar, wheat or any other commodity by taking a handful of it from the bag and then decide to purchase it or not. A housewife normally tests the cooked products to find if they are properly cooked and contain the proper quantity of salt.
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