There are also factors that determine sample sizes in qualitative studies. These
factors include the scope of the study, the phenomenon being investigated, the
quality of data collected, and the study design. The size of the sample is sufficient
when qualitative researchers achieve data saturation. Saturation means that
collecting data from additional participants adds no new information to what
has already been collected (Fawcett & Garity, 2009). Researchers should provide
information about sample selection so that nurses can make determinations
about the adequacy of the sample. Because the focus is on the data collected,
the richness of data, and the researchers’ conclusions, qualitative studies tend
to have smaller samples than quantitative studies do.
Recruitment and Retention of Subjects
Effective recruitment and retention of subjects are imperative to the credibility of
research studies. Failure to attend to recruitment and retention details can critically
affect the size of samples. Initial contacts made by researchers may determine
whether subjects will participate and remain in the study. Because researchers
may have only one opportunity to encourage participation, information should
be professional, informative, and culturally sensitive for the accessible popula-
tion. Flyers, letters, and advertisements are all methods used to recruit subjects.
Decisions about recruitment strategies are based on cost, predicted suc-
cess, and appropriateness for the accessible population. Recruitment materials
should include a brief description of the study purpose, inclusion criteria, and
information explaining how to enroll in the study. It is helpful to indicate in
recruitment materials if incentives are being offered for participation. Research-
ers should determine reasons that subjects elect not to participate in studies.
Being cognizant of who is not participating in a study should be included in
the discussion of the results because selection bias affects generalizability of
the results. Even with mailed, anonymous questionnaires, researchers may dis-
cover, by trending demographic data, similarities among subjects who did not
respond. Researchers should be aware that certain age groups, socioeconomic
groups, or ethnic groups may be underrepresented.
It is important to retain subjects after they have been recruited to participate
in a study. Strategies to reduce threats of mortality can be effective in reducing
subject attrition. Reasons why subjects withdraw from
studies should be monitored, and conditions causing
subjects to withdraw should be modified if possible.
Considerations for EBP
It is imperative that nurses use the best possible evidence to
make decisions about clinical practice. When considering
research studies for EBP, nurses must critically appraise
KEY TERM
data saturation: In
qualitative research,
the time when no
new information
is being obtained
and repetition
of information is
consistently heardFYI
Various factors determine sample sizes for
quantitative and qualitative studies, including
homogeneity or diversity of the population,
purpose of the study, focus of the study, design
of the study, and number of variables being
investigated. Sample size must be sufficient
to adequately support each of these factors.11.3 Sample Size: Does It Matter? 301