3.1.3 Theoretical basis of sampling
On the basis of sample study we can predict and generalize the behaviour of mass phenomena. This is possible because there is no statistical population whose elements would vary from each other without limit. For example, wheat varies to a limited extent in colour, protein content, length, weight, etc., it can always be identified as wheat. Similarly, apples of the same tree may vary in size, colour, taste, weight, etc., but they can always be identified as apples. Thus we find that although diversity is a universal quality of mass data, every population has characteristic properties with limited variation. This makes possible to select a relatively small unbiased random sample that can portray fairly well the traits of the population.
There are two important laws on which the theory of sampling is based:
1. Law of ‘Statistical Regularity’, and
2. Law of ‘Inertia of Large Numbers’,