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Evid Based Nurs 2:68-70 doi:10.1136/ebn.2.3.68

If you could just provide me with a sample: examining sampling in qualitative and quantitative research papers

  1. Carl Thompson, RN, PhD
  1. Centre for Evidence Based Nursing, Department of Health Studies, University of York, York, UK

      When undertaking any research study, researchers must choose their sample carefully to minimise bias. This paper highlights why practitioners need to pay attention to issues of sampling when appraising research, and discusses sampling characteristics we should look for in quantitative and qualitative studies. Because of space restrictions, this editorial focuses on the randomised controlled trial (RCT) as an example of quantitative research, and grounded theory as an example of qualitative research. Although these 2 designs are used as examples, the general principles as outlined can be applied to all quantitative and qualitative research designs.

      What is sampling?

      Research studies usually focus on a defined group of people, such as ventilated patients or the parents of chronically ill children. The group of people in a study is referred to as the sample. Because it is too expensive and impractical to include the total population in a research study, the ideal study sample represents the total population from which the sample was drawn (eg, all ventilated patients or all parents of chronically ill children). This point—that studying an entire population is, in most cases, unnecessary—is the key to the theory of sampling. Sampling means simply studying a proportion of the population rather than the whole. The results of a study that has assembled its sample appropriately can be more confidently applied to the population from which the sample came. Using the examples of samples provided at the start of the paragraph, we can see that Chlan sampled 54 patients from a population of patients who required mechanical ventilation,1(see Evidence-Based Nursing 1999 April, p49) whereas Burke et al sampled 50 children (and their parents) from a population of all children requiring admission to hospital for chronic health conditions.2(see Evidence-Based Nursing 1998 July, p79) In both studies the researchers wanted to …

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