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Judgment sampling or purposive sampling, where the researcher chooses the sample based on who they think would be appropriate for the study. This is used primarily when there is a limited number of people that have expertise in the area being researched, or when the interest of the research is on a specific field or a small group.
Nonprobability sampling methods include convenience sampling, quota sampling, and purposive sampling. In addition, nonresponse effects may turn any probability design into a nonprobability design if the characteristics of nonresponse are not well understood, since nonresponse effectively modifies each element's probability of being sampled.
In sociology and statistics research, snowball sampling [1] (or chain sampling, chain-referral sampling, referral sampling [2] [3]) is a nonprobability sampling technique where existing study subjects recruit future subjects from among their acquaintances. Thus the sample group is said to grow like a rolling snowball.
A judgment sample, or expert sample, is a type of non-random sample that is selected based on the opinion of an expert.. Results obtained from a judgment sample are subject to some degree of bias, due to the sample's frame (i.e. the variables that define a population to be studied) and population not being identical.
Bias in surveys is undesirable, but often unavoidable. The major types of bias that may occur in the sampling process are: Non-response bias: When individuals or households selected in the survey sample cannot or will not complete the survey there is the potential for bias to result from this non-response.
In the design of experiments, consecutive sampling, also known as total enumerative sampling, [1] is a sampling technique in which every subject meeting the criteria of inclusion is selected until the required sample size is achieved. [2]
Theoretical sampling has inductive as well as deductive characteristics. [6] It is very flexible as the researcher can make shifts in plans and emphasize early in the research process so that the data gathered reflects what is occurring in the field. [7] Certain disadvantages may be associated with this sampling method.
In one-dimensional systematic sampling, progression through the list is treated circularly, with a return to the top once the list ends. The sampling starts by selecting an element from the list at random and then every k th element in the frame is selected, where k, is the sampling interval (sometimes known as the skip): this is calculated as: [3]