Distinguish between random sampling and non-random sampling.
Random sampling: Random sampling is a technique of drawing a sample from the population in which each and every unit of the population has an equal chance of being selected in the sample.
Non-Random sampling: In a non-random sampling method, all the units of the population do not have an equal chance of being selected and convenience or judgement of the investigator plays an important role in the selection of the sample. They are mainly selected on the basis of judgement, purpose, convenience or quota.