ABSTRACT
Suppose it is considered important to gather ideas about, for example, (1) the total quantity of food grains stocked in all the godowns managed by a state government, (2) the total number of patients admitted in all the hospitals of a country classified by varieties of their complaints, (3) the amount of income tax evaded on an average by the income earners of a city. Now, to inspect all godowns, examine all admission documents of all hospitals of a country, and make inquiries about all income earners of a city will be too expensive and time consuming. So it seems natural to select a few godowns, hospitals, and income earners, to get all relevant data for them and to be able to draw conclusions on those quantities that could be ascertained exactly only by a survey of all godowns, hospitals, and income earners. We feel it is useful to formulate mathematically as follows the essentials of the issues at hand common to the above and similar circumstances.
