In judgemental sampling, the choice of sample items depends exclusively on the judgement of the investigator. This means that the investigator includes those sample points which he feels are representative of the population under study. For example, if the researcher wants to investigate the study habits of 100 students in a class, he may exercise his own judgement and choose 10 students who, in his opinion, are representative of the entire class.
Another example of judgemental sampling is in archaeology. An archaeologist does not choose the site of excavation randomly. He uses his knowledge of the history of the area and exercises judgement in order to choose which site to excavate.
The principles of sampling theory cannot be applied to judgement sampling, since it is not a random sampling method. Judgemental sampling is used to solve many times of problems in economics and business.
Advantages of Judgemental Sampling:
- When there are only a small number of sampling units, random selection may miss some important representative elements, whereas, judgement sampling will definitely include those units.
- We can obtain an even more representative sample if we divide the population into groups of different kinds and choose some sample units from each of the groups by judgement sampling.
Disadvantages of Judgemental Sampling:
- This main disadvantage of this method is that the sample may be affected due to the bias of the investigator. There is a risk that the investigator may try to choose a sample in such a way so as to establish his own preconceived opinions. For example, if an investigator wants to establish that the workers in a factory are earning low wages, he may choose a sample in such a way so that only people with low wages are included in the sample.
- There is no objective wat of evaluating the effectiveness of this sampling method. For random sampling methos such as cluster sampling and stratified sampling it is possible to calculate the sampling error of our estimate which is not possible in judgement sampling. If the individual making the decisions is knowledgeable and has good judgement then the results may be correct, otherwise the conclusion based on the sample will be erroneous.