If you want to define the target population then you will have to make use of sampling. If whole of the population is available for conduction research then it is known as census study. Samples are obtained when it gets impossible to conduct a survey or to test everyone in a group. Sampling technique is used to refer to the decision that who will be included in sampling process. The results are obtained on the basis of conclusions that will be representing an entire population. There are two ways through which you can do sampling. These methods are probability sampling and non-probability sampling. In probability sampling technique, you can select the target population through the random method. In order to prepare randomized samples, you need to ensure that everybody in population gets an equal chance to get selected. Another method of sampling is non-probability sampling. This method will not be involving the random sampling. According to researchers random sampling is considered to be more reliable. It is not a practical technique or nor it is sensible to use this.

There are different techniques of non-probability sampling. These techniques are purposive sampling or accidental sampling. In the method of purposive sampling, researcher will be choosing the sample on its own; this is due to the reason that there is very limited number of subjects. For instance- if you are carrying out the study about zoologists and if there are 12 zoologists in your scope area then you can choose 12 in your sample. This sampling technique is used when you want to access any particular subset. You should make sure that you are rejecting all those people who do not fit in to yours profile. You make use of purposive sampling technique when you will be having a purpose in your mind. You need to select only those people that will suit your purpose and reject all those which do not go with the purpose. As this sampling technique is a non-probability technique, so it can be subjected to various bias and errors. This sampling technique is used by many magazines as well as newspapers. You will also find that many market researchers making use of this sampling technique who wants to have a support for their product. This sampling technique usually starts with approaching those people who are present in the street and then moving on to yours likely suspect and then rejecting those people who do not suit this method.