TYPES OF SAMPLING:

Sampling plans can be  grouped under two categories-probability  sampling and non-probability sampling. Probability sampling uses a technique by which the researcher ensures the probability,  that  each element of p~pulation will  be  included in the sample. That  is each element has  an equal or known chance of being included.  It utilizes some form of random selection because of which  greater confidence can be  placed  in  the representativeness  of probability samples. Non-probability  samples use non-random methods  i.e.  there  is bias in the selection. There is no  assurance that every element has a chance  of being included or,  in other words the researcher cannot estimate the probability that each element will be  included in the sample. Refer  to Figure 4.1 and note the purpose of probability  and non-probability sampling. The population values such as mean of standard deviation  is  called a Parameter whereas the measured value of the sample is termed statistic. We infer the parameter from the statistic when we know that the sample  is  a true representative of population. Refer Block 4  for  further details of parameter  and statistic.