Simple Random Sampling
Lest there be any doubt, we stress that a random sample is not a sample taken in a haphazard way! On the contrary, much care is required. A random sample is one taken such that every item in the population defined in the research has an equal chance of being selected. This can be a demanding definition to put into practice in many research projects! Furthermore, there is a complication concerning what is known as unrestricted random sampling, to which most statistical theory relates.
Unrestricted Random Sampling is carried out with replacement, i.e. the item selected at each draw is ‘returned’ to the population before the next draw is made. Thus any given unit can appear more than once in a sample.
Simple Random Sampling is random sampling without replacement, and this is the form of random sampling most used in practice.
A sampling frame is the first requirement in order to implement simple random sampling. The selection of respondents or items from the frame can then be accomplished using the instruction provide with most tables of random numbers. The procedure is simple. If N members in a population are assigned a series of numbers, and n of them are selected by random sample of the size determined by the researcher. Although a random sample is simple conceptually, it may not be the most efficient or convenient way to carry out a research survey as will become apparent in the following sub-sections.