Ch. 11 - Sampling: Quantitative and Qualitative Approaches

Probability sampling

The use of random procedures to select a sample that can allow us to estimate the expected degree of sampling error in a study and determine or control the likelihood of specific units in a population being selected for the study.

random sampling

A precise, scientific procedure for selecting research population elements for a sample that guarantees an equal probability of selection of each element when substantial samples are selected from large populations.

quota sampling

A type of nonprobability sampling in which units are selected into the sample on the basis pf prespecified characteristics so that the total sample will have the same distribution of characteristics as are assumed to exist in the population being studied.

Element

The unit selected in a sample about which information is collected.

Population

The theoretically specified aggregation of study elements

study population

The aggregation of elements from which the sample is actually selected.

Random selection

A sampling method in which each element has an equal chance of selection independent of any other event in the selection process.

Sampling unit

An element or set of elements considered for selection in some stage of sampling.

Parameter

The summary description of a given variable in a population.

sampling error

The difference between the true population parameter and the estimated population parameter.

Sampling frame

The list or quasi-list of elements from which a sample is selected.

simple random sampling

Using a table of random numbers to select sampling units after assigning a single number to each element in the sampling frame list.

Systematic sampling

An efficient alternative to random sampling, in which every kth element in the sampling frame list - after a random start - is chosen for inclusion in the sample.

sampling interval

the standard distance between elements selected in systematic sampling

Sampling ratio

The proportion of elements in the population that are selected in a systematic sample.

cluster sampling

A multistage sampling procedure that starts by sampling groups (clusters) of elements in the population and them subsampling individual members of each selected group afterward.

nonprobability sampling

the use of procedures to select a sample that does not involve random selection

Availability sampling

A sampling method that selects elements simply because of their ready availability and convenience. Frequently used in social work because it is usually less expensive than other methods and because other methods may not be feasible for a particular type of study population.

purposive sampling

selecting a sample based on your own judgment about which units are most representative or useful

Deviant case sampling

A form of purposive sampling in which cases that don't fit into regular patterns are selected to improve understanding of regular patterns.

snowball sampling

A nonprobability sampling method used when the members of a special population are difficult to locate. Each selected member of the target population whom one is able to locate other members of that population that they happen to know.

Intensity Sampling

A qualitative sampling technique similar to deviant case sampling in which cases are selected that are more or less intense than usual, but not so unusual that they would be called deviant.

Theoretical sampling

A sampling method associated with the grounded theory paradigm of qualitative research, in which new cases are selected that seem to be similar to those that generated previously detected concepts and hypotheses, but once the researcher perceives that no new insights are being generated from observing similar cases, a different type of case is selected, and the same process is repeated until the observation of different types of cases seems to be generating no new insights.