ABSTRACT
In random sampling, every unit in the population has a known probability of being included in the sample. The sampling bias is nothing but consistent errors that arise due to the sample selection. It may be due to wrong demarcation of the sample from the population, measuring the succeeding or proceeding units in the list, and the errors of estimation. Several random sampling methods are available depending on the objectives of the study, the size and nature of the population, required precision of the estimates, sanctioned budget, and the availability of the sampling frame. A sampling frame is a list of all the units in the population listed alphabetically or chronologically and numbered serially. Area sampling is close to cluster sampling, which is more suitable for mental morbidity surveys. The mental morbidity surveys in India adapted the schemes of selection of study areas/sampling procedures depending on the nature of the population.
