What is Probability samplings are all except and explain in detail?
SAMPLING When a large propoion of individuals or items or units have to be studied, we take a sample. It is easier and more economical to study the sample than the whole population or universe. Great care therefore is taken in obtaining a sample. It is impoant to ensure that the group of people or items included in the sample are representative of the whole population to be studied Sampling Methods The following three methods are most commonly used : (1) Simple random sample : This is done by assigning a number to each of the units (the individuals or households) in the sampling frame. A table of random numbers is then used to determine which units are to be included in the sample. Random numbers are a haphazard collection of ceain numbers, arranged in a cunning manner to eliminate personal selection of unconscious bias in taking out the sample. With this procedure, the sample is drawn in such a way that each unit has an equal chance of being drawn in the sample. This technique provides the greatest number of possible samples. (2) Systematic random sample : This is done by picking every 5th or 10th unit at regular intervals. For example, to carry out a filaria survey in a town, we take 10 per cent sample. The houses are numbered first. Then a number is selected at random between 1and10 (say four). Then every 10th number is selected from that point on 4, 14, 24, 34, etc. By this method, each unit in the sampling frame would have the same chance of being selected, but the number of possible samples is greatly reduced. (3) Stratified random sample : The sample is deliberately drawn in a systematic way so that each poion of the sample represents a corresponding strata of the universe. This method is paicularly useful where one is interested in analysing the data by a ceain characteristic of the population, viz. Hindus, Christians, Muslims, age-groups etc. as we know these groups are not equally distributed in the population. It is useful to note at this stage that Greek letters are usually used to refer to population characteristics : mean (u), standard detion (cr), and Roman letters to indicate sample characteristics: mean ( x), standard detion (s). Ref : Park 23rd edition Pgno : 849