55 In addition, a researcher cannot exclude a subset of people from selection as subjects because he or she does not agree with them, does not like them, or finds them hard to deal with. Reasons for withdrawal included the desire for a different exercise program (n = 7); insufficient time (n = 6); intolerance to meds (n = 5); cancer recurrence (n = 5); health problems (n = 2); and relocation (n = 1). (Twiss et al., 2009, p. 22) 43 Another technique is to assign a number to each name in the sampling frame. Importantly, these types of studies do not focus on reasons for the occurrence of the phenomenon. Sample attrition should be reported in the published study to determine if the final sample represents the target population. Qualitative research 3rd ed. Researchers need to provide logical reasons for their inclusion and exclusion sampling criteria, and certain groups should not be excluded without justification. Theoretically, to obtain a probability sample, the researcher must develop a sampling frame that includes every element in the population. From a sampling theory point of view, randomization means that each individual in the population should have a greater than zero opportunity to be selected for the sample. Sampling strategies have been devised to accomplish these three tasks and to optimize sample selection. The second situation is in cases in which the individual elements making up the population are unknown, preventing the development of a sampling frame. 4. The sampling method implemented in a study varies with the type of research being conducted. Addressing Bias in Electronic Health Record-Based Surveillance of Cardiovascular Disease Risk: Finding the Signal Through the Noise. Because this is a quasi-experimental study that examined the impact of the treatment on the dependent or outcome variables, the increased controls imposed by the sampling criteria strengthened the likelihood that the study outcomes were caused by the treatment and not by extraneous variables. Before Values of individual subjects vary from the value of the sample mean. Sample surveys. One of the most important surveys that stimulated improvements in sampling techniques was the U.S. census. The NHIS [National Health Interview Survey] methodology employs a multistage probability cluster sampling design [sampling method] that is representative of the NHIS target universe, defined as the civilian noninstitutionalized population (Botman, Moore, Moriarty, & Parsons, 2000, p. 14; National Center for Health Statistics). Sample attrition rate is calculated by dividing the number of subjects withdrawing from a study by the sample size and multiplying the results by 100%. Selecting the sample for a research study. The accessible population must be representative of the target population. 16. All of these factors limit representativeness and limit our understanding of the phenomena important in practice. Non-probability sampling involves non-random selection based on convenience or other criteria, allowing you to easily collect data. Twiss et al. At this level, either all the patients on the nursing unit who fit the criteria for the study might be included, or patients could be randomly selected. Key concepts of sampling theory include populations, target population, sampling or eligibility criteria, accessible population, elements, representativeness, sampling frames, and sampling methods or plans. That said, the researcher must be alert to a number of methodological and ethical pitfalls associated with recruitment and retention.18 Recruitment techniques such as monetary incentives for participation may bias the study outcome; and the extent that subjects systematically discontinue participation in the study may disrupt the balance of the study sample, creating threats to generalizability and study validity. Confused about theoretical sampling? The population is a particular group of people, such as people who have had a myocardial infarction, or type of element, such as nasogastric tubes, that is the focus of the research. However, some of the outcomes are more valid than others, partly because of the sampling techniques used. Some populations are elusive and constantly changing. Boston: Cengage Learning; 2006. p. 76396. AJN The American Journal of Nursing121(3):53-57, March 2021. Probability sampling methods have been developed to ensure some degree of precision in estimations of the population parameters. In cluster sampling, the researcher develops a sampling frame that includes a list of all the states, cities, institutions, or organizations with which elements of the identified population would be linked. The selection included all of the most populous primary sampling units in the United States and stratified probability samples (by state, area poverty level, and population size) of the less populous ones. The sampling frame in this study included the names of the 746 RNs who were asked to participate in the study. Disclaimer. For a study examining the relationship between patient satisfaction and triage nursing care in the ED, researchers randomly sampled every fifth person who presented to the ED. These values do not vary randomly around the population mean. Sampling error is usually larger with small samples and decreases as the sample size increases. Wolters Kluwer Health The researcher selects subjects from the sampling frame using a sampling plan. For a sample to be representative, it must be similar to the target population in as many ways as possible. In a third step, clusters of dwelling units form the secondary sampling units selected from each substratum [3rd stage cluster sampling]. Moving the pencil or finger up, down, right, or left, the researcher uses the numbers in order until the desired sample size is obtained. Figure 15-1 shows the relationships among the population, target population, and accessible populations. In sampling methods, parameters of the population are estimated from the sample drawn from the population. For example, the researcher places a pencil on 58 in Table 15-2, which is in the fourth column from the left and fourth row down. Sampleretentionrateformula=numbersubjectscompletingstudysamplesize100% In some studies, the entire population is the target of the study. Sampling theory in nursing research is the process of grouping a set of individuals, events, behaviors, or other items to investigate. This situation could occur, for example, if all the subjects were college students, which has been the case in the development of many measurement methods in psychology. Application of simple random sampling and the attrition of only three (4%) subjects from the study seem to provide a sample representative of the target population. (2006) used a stratified random sampling method to obtain their sample of nurse practitioners (NPs) and physician assistants (PAs) for the purpose of studying the ethical conflict of these healthcare providers associated with managed care. The likelihood is increased that the sample is representative of the target population and the results are an accurate reflection of reality. Variables commonly used for stratification are age, gender, ethnicity, socioeconomic status, diagnosis, geographical region, type of institution, type of care, care provider, and site of care. Today, federal funding for research is strongly linked to including these populations in studies. Gray JR, et al. 19 For example, numbers are assigned to medical records, organizational memberships, and professional licenses. Sample selection is a very important but sometimes underestimated part of a research study. While less expensive, nonprobability sampling techniques are prone to selection bias and often do not produce a sample that fully represents the target population. The sample selection strategy (the sampling plan) is constructed with the intent to minimize selection bias in the selection of participants from within the sampling frame. The sampling strategy employed is of utmost importance to ensure that a representative sample of participants is chosen. 2021 Jan 1;121(1):64-67. doi: 10.1097/01.NAJ.0000731688.58731.05. While the purpose of stratified random sampling is to improve participant representation, the purpose of cluster sampling is to improve sampling efficiency, thus reducing time and cost.3. The comparison group retention was 113 women with a retention rate of 90% (113 125 = 90.4% = 90%). In addition, a researcher cannot exclude a subset of people from selection as subjects because he or she does not agree with them, does not like them, or finds them hard to deal with. Representativeness is usually evaluated by comparing the numerical values of the sample (a statistic such as the mean) with the same values from the target population. Cluster sampling Common methods of probability sampling include the following6: In simple random sampling, study participants are randomly selected from the sampling frame using a randomization mechanism, as previously discussed. These inclusion and exclusion sampling criteria were appropriate for the study to reduce the effect of possible extraneous variables that might have an impact on the treatment (ST exercises) and the measurement of the dependent variables (muscle strength, balance, and falls). Related Sampling Theory. Sampling theory was developed to determine mathematically the most effective way to acquire a sample that would accurately reflect the population under study. To use a table of random numbers, the researcher places a pencil or a finger on the table with the eyes closed. Stratified random sampling is used when the researcher knows some of the variables in the population that are critical to achieving representativeness. The retention rate is calculated by dividing the number of subjects completing the study by the initial sample size and multiplying by 100%. 63 Because it is impossible to know the sampling error exactly, all sampling errors are approximate and are based on a calculation called the standard deviation. However, the sample was a great strength of this study and appeared to represent the target population of NPs and PAs currently practicing in primary care in the United States. Knowledge of sampling methods is essential to design quality research. In studies involving a treatment, subjects in the control group who do not receive the treatment may be more likely to withdraw from the study. What Is Sampling Theory in Nursing Research? About 1,300 staff RNs [population] were employed at the hospital at the time of the study. A total of 746 RNs who met eligibility criteria were invited to participate in the study [sampling frame of target population]. 63 18. What Adult Electrocardiogram (ECG) Diagnoses or Findings are Most Important for Advanced Care Paramedics to Know? Sampling error limits generalizability and research accuracy (validity) by introducing bias into the study. (2009) conducted a quasi-experimental study to examine the effects of strength and weight training (ST) exercises on muscle strength, balance, and falls of breast cancer survivors (BCSs) with bone loss (population). official website and that any information you provide is encrypted It is from the sample that data is collected in the course of a study, and because that sample is representative of the population, the results can be generalized to the population in a scientific study. 88 Nonprobability sampling. Patient volume, staffing, and workload in relation to risk-adjusted outcomes in a random stratified sample of UK neonatal intensive care units: a prospective evaluation. To accomplish this goal, the researcher must acquire a list of every member of the population through the use of the sampling criteria to define membership. Stratification is not as useful if one stratum contains only a small number of subjects. Again, these units could be people, events, or other subjects of interest. This listing of members of the population is referred to as the sampling frame. Djukic, Kovner, Budin, and Norman (2010) studied the effect of nurses perceived physical work environment on their job satisfaction and described their sampling frame in the following excerpt. Today, federal funding for research is strongly linked to including these populations in studies. Each member of the sampling frame has only one chance of being chosen for inclusion in the study sample.4 For example, suppose a nurse researcher is interested in workplace satisfaction among the 200 medicalsurgical nurses within a health care system. The eligible RNs were those who had a functioning work e-mail account and who worked fulltime, on inpatient units, providing direct patient care. (Djukic et al., 2010, pp. maintain their nursing identity and further their efforts for developing a nursing specialty. 10 The term used by researchers depends of the philosophical paradigm that is reflected in the study and the design. Abstract. The study was conducted in obstetric intensive care units and services of all the public and university hospitals in the province of Eskisehir, Turkey. During the 4 month study, 281 patients attended for the cesarean operations to the obstetric intensive care units and services of all hospitals concerned [target population and settings].
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