Non-Probability/ Non-random sampling Methods
1. Convenience Sampling: In this sampling, the sample units are selected with the convenience of Investigator. Convenient samples are selected neither by probability nor by judgment.
Merit: Useful in pilot survey
Demerit: 1. Results usually biased and
2. Unsatisfactory
2. Quota Sampling: Most commonly used in non-probability sampling. The population is first segmented into mutually exclusive sub-groups, then judgment is used to select subjects or units from each segment based on a specific proportion.
Eg: 1. In a radio-listening survey, the organization told to interview persons, out of every 100 persons, 60 are to be housewives, 25 farmers and 15 are children under age 15 years.
2. Public opinion studies.
3. Judgment Sampling: In this method of sampling the choice of sample items depends exclusively on the judgment of the investigator. It is used when the investigator thinks to be most typical to select samples from the Universe.
eg: 1. 10 students are to be selected from a class of 60 for analyzing the spending habits of students, the investigator would select 10 students who, in his opinion, are representative of the class.
Merits: 1.When only a small number of units are in the universe, SRS may miss the more important elements, where judgment selection would certainly include them in the sample.
2. When we want to study some unknown traits of population, some of whose characteristics are known, we may then stratify the population according to these known properties and select sampling units from each stratum on the basis of judgment. This method is used to obtain a more representative sample.
Limitations: 1.This method is not scientific because the population units to be sampled may be affected by personal bias of the investigator.
2. There is no objective way of evaluating the reliability of sample results. The success of this method depends on the excellence in judgment.
4. Snowball Sampling/C0ld-calling/Chain sampling/ Chain referral sampling:
It is used where potential participants are hard to find. Snowball literally means once you have the ball rolling, it picks up more “snow” along the way and becomes larger and larger. A special non probability method used when the desired sample characteristic is rare. The research starts with a key person and introduces the next on to become a chain.
Merits: 1. When the lack of desired sample/ participants
2. It may help to discover characteristics about a population that weren’t aware existed.
Limitations: 1.It is not possible to determine sampling errors or make inference about population based on the obtained sample.
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