Evidence-Based Practice for Nurses

discusses the elements of a study. The term population is
used appropriately when one is generalizing findings to
all possible elements (Bloom & Trice, 2011).

The Hallmark of a Sample:

Representativeness

Researchers place much importance on representative-
ness. This means obtaining representative samples so that
results of studies can be generalized to target popula-
tions (Albert, O’Connor, & Buelow, 2012). Generalizability, also referred to
as external validity, is the applicability of study findings to target populations.
There is greater concern for generalizability in quantitative research studies
than in qualitative studies. Generalizabilty of study findings is a critical fac-
tor in EBP. As nurses identify and read research studies to determine best
practice, they must determine whether results of the studies are applicable
to patients in their organizations. Confidence in generalizability can be in-
creased if samples accurately represent the target population. This means that
the elements of a sample must possess characteristics similar to the elements
composing the target population (see Figure 11-2). Melnyk and Cole (2011)
identified a four-step method to ensure that samples are representative of
target populations (see Box 11-1). By following this process, the potential
for obtaining a representative sample is high. When the population, target
population, accessible population, and sample are similar, the sample can be
said to be representative.

Inclusion criteria are used to determine subjects to be included in the
sample. Researchers identify characteristics that each element must possess to
be included in the sample. Inclusion criteria are guided by the research question
and careful identification of the target and accessible populations. For example,
in the study of adolescent diabetics, the researcher would first identify the
essential characteristics or inclusion criteria for the target population. These
characteristics could include age, a diagnosis of type 1 diabetes, receiving care
at a local diabetic clinic, and ability to speak English. Researchers often report
inclusion criteria to clearly identify the subjects of the study.

The next time you use the term sample or population, pause and consider whether you have

used the term correctly. Were you referring to the individuals who participated in a study or

were you referring to the group of individuals to whom the findings would be generalized?

Listen to how others use these terms. Are they using them correctly?

CRITICAL THINKING EXERCISE 11-1

KEY TERMS

representativeness:

The degree to

which elements of

the sample are like

elements in the

population

inclusion criteria:

Characteristics

that each element

must possess to

be included in the

sample

FYI

In order to collect evidence that changes

clinical practice, nurses must identify and

appraise research that is relevant to clinical

practice. Key to this appraisal is determining

that the sample and the sampling method

are appropriate for the study and generaliz-

able. Confidence in generalizability can be

increased if samples accurately represent

the target population.

11.1 Fundamentals of Sampling 287