What is the Method of Non-Random Sampling?



There are three methods of non-random sampling, as follows:

(i) Judgment Sampling (Purposive Sampling):

In this method, the choice of sample items depends upon the judgment of the investigator. The investigator uses his judgment in the choice and includes those items that he thinks are most typical of the universe and have the qualities needed for his research project. Example: The researcher wants to select 10 students from a class of 60 students for studying the spending habits of students. He would select those 10 students who, in his opinion, represent the entire class. It is up to him to select or reject the students for the purpose of forming such a sample.

The method has many advantages. Firstly, it is useful if the universe has a small size. Accordingly, the researcher would include these items, which are vital for his research. Secondly, he can study the unknown characteristics of population with the help of known characteristics. He would divide the population according to the known characteristics and select sampling units from each division on the basis of his judgment. Thirdly, business executives and officials of the public sector do not have time to solve everyday problems. Hence, judgment sampling is the only practical method to arrive at a solution to solve such problems as need urgent solutions.

The method is not sans limitations. Firstly, it is not a scientific modus operandi. Secondly, the personal prejudice or bias of the researcher may affect the sample. Thirdly, the researcher may define some basic ideas or presuppositions about his study and then, include only those items that are conforming to his presuppositions. So, an element of subjectiveness creeps in. Fourthly, even if the judgment sample represents the given population, we cannot determine the sampling errors in an objective manner.

(ii) Convenience Sampling:

A convenience sample is obtained by selecting convenient population units. This method is also called Chunk. We select a small traction of the total population only on the basis of our convenience. We do not use probability, judgment or any other method. These samples can have bias because the researcher would like to select only those elements that are convenient for him to choose.

Thus, the chosen elements could be different from most of the elements of the population. The results obtained by working on a convenience sample can hardly represent the characteristics of the population. However, this method is useful for pilot studies. Example- Suppose that a person is required to submit a project report on labour-management relations in the textile industry. He would go to a textile mill, which could be near his office. He would interview some people from that mill; naturally, they should be easily available.

(iii) Quota Sample:

This is type of judgment sampling. Here, quotas are set according to some characteristics of the population. These characteristics could be income groups, age, religion, political party, race, caste, amount to be spent on an item, number of programmes watched on TV, number of people checking into a hotel during the off-season, tourist spots receiving most of foreign visitors, etc.

The researcher arranges some interviewers who are given some quotas. Each interviewer is supposed to select some elements for his sample; this number is his quota. Within this quota, the interviewer can select the sample on the basis of personal judgment. Example- In a marketing research survey, interviewers is supposed to select 500 people from Oklahoma City.

Out of every 100 persons, 60 must be housewives, 25 must be businessmen and 15 must be children under the age of 10 years. Within these quotas, the interviewer is free to select the people for his sample. The cost per person interviewed is very low. But because of personal judgment, personal bias may creep in and eventually, lead to wrong results.