The use of samples in research is usually followed by the calculation of sample estimates with the aim of either estimating the values of population parameters from sample statistics or testing statistical hypotheses about population parameters. These two aims require that the researcher has accurate knowledge of the values of sample statistics as estimates of the relevant population parameters. Based on this background, this essay endeavors to discuss the sampling procedures/techniques that are commonly used in educational research under the two categories which are Probability and Non-probability sampling procedures. Further, it will highlight the strengths and weaknesses of using the sampling procedures it will have identified.
Probability sampling techniques are primarily used in quantitatively oriented studies and involve "selecting a relatively large number of units from a population, or from specific subgroups (strata) of a population, in a random manner where the probability of inclusion for every member of the population is determinable'' (Tashakkori & Teddlie, 2003: 713).
Probability samples aim to achieve representativeness, which is the degree to which the sample accurately represents the entire population. A probability sampling scheme is one in which every unit in the population has a chance (greater than zero) of being selected in the sample, and this probability can be accurately determined.
Non-probability type of sampling is where a sample is drawn on the basis of opportunity. For example, the sample could include such things as youths attending a school activity, service providers attending a conference or parents attending a school event, (Reinard; 2008). The sampling techniques where some fundamentals of the public have no chance of selection are sometimes referred to as 'out of coverage', or where the probability of selection cannot be accurately determined. It involves the selection of elements based on assumptions regarding the population of interest which forms the...