1 E X E R C I S E 2 Identifying Probability and Nonprobability Sampling Methods in Studies Statistical Technique in Review A sampling method is the process of selecting people, events, behaviors, or other elements that are representative of the population being studied ( Grove, Burns, & Gray, 2013 ). The sampling methods implemented in research are usually categorized as either probability or nonprobability. Researchers select a sampling method for their study based on the study problem and purpose, population studied, and their own expertise and experiences. Table 2-1 identifies the common probability and nonprobability sampling methods applied in quantitative, qualitative, and mixed methods studies in nursing ( Thompson, 2002 ). Quantitative research is an objective research methodology used to describe, examine relationships or associations among, and determine cause-and-effect interactions between variables ( Shadish, Cook, & Campbell, 2002 ). Qualitative studies are subjective and are conducted to describe and give meaning to life experiences, cultures, or historical events ( Marshall & Rossman, 2016 ; Munhall, 2012 ). Mixed methods studies include methodologies from both quantitative and qualitative research ( Creswell, 2014 ). TABLE 2-1 PROBABILITY AND NONPROBABILITY SAMPLING METHODS COMMONLY USED IN NURSING STUDIES Sampling Method Common Application(s) Probability Sampling Methods Simple random sampling Quantitative studies Stratified random sampling Quantitative studies Cluster sampling Quantitative studies Systematic sampling Quantitative studies Nonprobability Sampling Methods Convenience sampling Quantitative, qualitative, and mixed methods studies Quota sampling Quantitative and mixed methods studies Purpose or purposeful sampling Qualitative, mixed methods, and some quantitative studies Network or snowball sampling Qualitative, mixed methods, and some quantitative studies Theoretical sampling Qualitative and mixed methods studies Probability Sampling Methods Probability sampling , also known as random sampling, requires that every member of the study population has an equal and independent opportunity to be chosen for inclusion in a study. Probability sampling involves identifying the sampling frame or each person or element in a study target population and then randomly selecting a sample from that population (see Exercise 3 ). Thus probability sampling allows every person or element of the study population to be represented without researcher bias and minimizes sampling error. The purpose of sampling in quantitative research is to obtain study participants who are as representative of the target population as possible. The sample's representativeness of the study population is increased by probability sampling. A large sample with limited a rition increases the representativeness of the sample ( Cohen, 1988 ). Four common sampling designs used to select random samples in quantitative studies include simple random sampling, stratified random sampling, cluster sampling, and systematic sampling (see Table 2-1 ; Grove et al., 2013 ;
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- researcher, random sampling, Nonprobability sampling , Nursing Research