Sampling theory was developed to determine the most effective way to acquire a sample that accurately reflects the population under study. Key concepts of sampling theory include populations, target population, sampling or eligibility criteria, accessible population, elements, representativeness, sampling frames, and sampling plans or methods.(Burns & Groves, 2013). A sampling plan or method outlines strategies used to obtain a sample for a study. Like a design, a sampling plan is not specific to a study. The plan is designed to increase representativeness and decrease systematic variation or bias. The sampling plan may use probability (random) or nonprobability (nonrandom) sampling methods. When critically appraising a study, identify the study sampling plan as either probability or nonprobability, and determine the specific method used to select a sample.
The research design, populations, and setting are important components that help answer the research questions and inform nurses if findings will be relevant to their practice. For nurses to be consumers of research, being able to critique the theory that is being tested, determine if the design is appropriate to answer the question and decide if the sample supports generalization, adds to knowldege translation and depth of research. To help determine when the research can be applied to their practice, they need to be able to assess these components for applicability to their practice and setting.