Evidence-Based Practice for Nurses

Nonprobability Sampling Methods

A second category of sampling methods is nonprobability sampling. These
methods do not require random selection of elements and therefore are less
likely to be representative of the target population. Researchers use nonprob-
ability sampling methods when a sampling frame cannot be determined.
Because randomization is not used, the threat of selection bias is increased;
therefore, samples selected using nonprobability are likely to be less repre-
sentative than are samples selected using probability methods. The researcher
should make every effort to create a representative sample and clearly describe
the method of sampling for the reader (Houser, 2011; Melnyk & Cole, 2011).
There are four nonprobability sampling methods: convenience, quota, pur-
posive, and theoretical. Table 11-3 provides an overview of nonprobability
sampling methods.

Convenience Sampling

In convenience sampling, also known as accidental sampling, researchers
select elements for inclusion in the sample because they are easy to access. For
example, a researcher desires to conduct a study of patients with type 2 diabetes
presenting for treatment at an emergency department. Because the researcher
cannot predict which diabetic patients will use the emergency department over
the course of the study, it is impossible for the researcher to create a sampling
frame and randomly select subjects. Therefore, the researcher elects to use a
convenience sample that includes all patients with type 2 diabetes who seek
care at the emergency department.

Although sampling bias is a concern with this method, strategies can be
used to control for bias. Comparing demographic data from individuals in the
sample to population demographics can help researchers determine whether
the sample is representative. Researchers should present a thorough descrip-
tion of the convenience sample in the study results and compare it to the target
population. A careful explanation of why and how the sample was selected
allows nurses to determine the potential for sampling bias and whether study
findings should be used as evidence for clinical practice.

Suppose you are on a task force at your university. The task force needs to survey students about

attitudes toward adopting a smoke-free campus. What are the advantages and disadvantages

to using each of the probability sampling methods?

CRITICAL THINKING EXERCISE 11-2

KEY TERMS

nonprobability

sampling: Sampling

methods that

do not require

random selection of

elements

convenience

sampling:

Nonprobability

sampling method

in which elements

are selected

because they are

easy to access

11.2 Sampling Methods 295