account of the fact that this population is divided into rural and urban sectors which are very different from each other. When considering the rural population of any one state, we have to allow for the fact that this population lives in villages of different sizes. In the same way, the population of a single village may be stratified by class, caste, gender, age, religion or other criteria. In short, the notion of stratification tells us that the representativeness of a sample depends on its being able to reflect the characteristics of all the relevant strata in a given population.
Which kinds of strata are considered relevant depends on the specific objectives of the research study. For example, when doing research on attitudes towards religion, it would be important to include members of all religions. When The Census and the National Sample Survey Organisation The population census of India conducted every ten years is the largest such exercise in the world. (China, the only country with a larger population, does not conduct a regular census.) It involves literally lakhs of investigators and a stupendous amount of logistical organisation not to speak of the huge expenditure incurred by the Government of India.
However, in return for this outlay, we get a genuinely comprehensive survey in which every household in India and every one of the more than one billion people living in India get included. Obviously, it is not possible to conduct such a gigantic survey very often; in fact, many developed countries no longer conduct a full census; instead they depend on sample surveys for their population data, because such surveys have been found to be very accurate. In India, the National Sample Survey Organisation (NSSO) conducts sample surveys every year on the levels of poverty and unemployment (and other subjects). Every five years it also conducts a bigger survey involving about .
lakh households covering more than lakh persons all over India. In absolute terms this is considered a large sample, and the NSSO surveys are among the biggest regularly conducted surveys in the world. However, since the