Non-probability Sampling
Non-probability sampling is based on the judgement of the researcher. The guiding factors in non-probability sampling include the availability of the units, the personal experience of the researcher and his/her convenience in carrying out a survey. Since these samples are not prepared through random sampling techniques, they are known as non-probability samples. Depending on the technique used, non-probability samples are classified as below:-
1. Convenience Sampling
In a convenience sampling method, the samples are selected from the population directly because they are conveniently available for the researcher. The samples are easy to select, and the researcher did not choose the sample that outlines the entire population.
In researching customer support services in a particular region, we ask your few customers to complete a survey on the products after the purchase. This is a convenient way to collect data. Still, as we only surveyed customers taking the same product. At the same time, the sample is not representative of all the customers in that area.
2. Consecutive Sampling
Consecutive sampling is similar to convenience sampling with a slight variation. The researcher picks a single person or a group of people for sampling. Then the researcher researches for a period of time to analyze the result and move to another group if needed.
The most common examples of a consecutive sample is when companies/ brands stop people in a mall or crowded areas and hand them promotional leaflets to purchase a luxury car.
3. Quota Sampling
In the quota sampling method, the researcher forms a sample that involves the individuals to represent the population based on specific traits or qualities. The researcher chooses the sample subsets that bring the useful collection of data that generalizes the entire population.
This technique is often used in market research because it is a cost and time-efficient way of recruiting a representative sample.
4. Purposive or Judgmental Sampling
In purposive sampling, the samples are selected only based on the researcher’s knowledge. As their knowledge is instrumental in creating the samples, there are the chances of obtaining highly accurate answers with a minimum marginal error. It is also known as judgmental sampling or authoritative sampling.
Examples of groups recruited through purposive sampling could be secondary school teachers or people receiving welfare benefits.
5. Snowball Sampling
Snowball sampling is also known as a chain-referral sampling technique. In this method, the samples have traits that are difficult to find. So, each identified member of a population is asked to find the other sampling units. Those sampling units also belong to the same targeted population.
This technique usually involves the researcher gaining the initial respondent''s trust and is often used in studies of criminal or deviant groups.
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