Quantitative Designs
By this point, you are familiar with quantitative methods and are ready to learn
to apply your knowledge about research principles to make decisions about the
evidence. A critical appraisal of quantitative studies is necessary for nurses to
determine the validity, reliability, statistical significance, clinical importance,
and applicability of the findings (University of Alberta, 2008a).
When appraising meta-analyses, nurses should establish whether well-
designed studies that fit with the research question are included. Both
published and unpublished studies should be included. One must be con-
fident that the literature was systematically searched to obtain an adequate
sample size. There should be evidence that statistical findings from the
studies were merged to identify incongruencies and similarities of findings
among the studies.
Other kinds of studies that nurses are likely to appraise are randomized
controlled trials (RCT). RCT sometimes also stands for randomized clinical
trials. Studies of this type can be found in the nursing literature and are espe-
cially important to the advancement of EBP. Studies showing that a treatment
has a greater effect, rather than studies showing a small effect, weigh more
heavily in the appraisal. Sample sizes are typically large, and often patients are
recruited from multiple sites. Studies are strengthened by using strategies such
as blinded designs, ensuring that interventions are controlled, and showing
that patient groups were similar at the beginning of the trial (University of
Alberta, 2008b). Reviewers should determine whether there is bias by using
the five Cs approach for evaluation: contamination, crossover, compliance,
cointervention, and count, that is, attrition (Attia & Page, 2001). Results
should be readily applicable to patients with similar clinical and demographic
backgrounds.
Cohort studies, sometimes known as quasi-experimental studies, examine
a large sample of the population and observe changes in characteristics over
time. Like RCTs, there are two groups: one that receives the treatment and one
that does not. Then both groups are followed for a period of time related to
the outcome of interest. Cohort studies are considered to be less rigorous than
RCTs are because subjects are not randomly assigned to groups; therefore, the
two groups may vary on other characteristics, and the controls may be difficult
to identify. Cohort studies may be retrospective or prospective.
Case control studies compare two groups: those who have a specific condition
and those who do not have the condition. This type of research usually focuses
on rare disorders or disorders where there is considerable time between expo-
sure or treatment and the onset or change in outcome. In case control studies,
fewer subjects are needed than in cross-sectional studies. The disadvantages of
KEY TERMS
meta-analyses:
Scholarly papers
that combine
results of studies,
both published and
unpublished, into a
measurable format
and statistically
estimate effects
of proposed
interventions
randomized
controlled trials:
Experimental
studies that
typically involve
large samples and
are conducted in
multiple sites
cohort studies:
Quasi-experimental
studies using two
or more groups;
epidemiological
designs in which
subjects are
selected based on
their exposure to a
determinant
case control
studies: A type
of retrospective
study in which
researchers begin
with a group
of people who
already had the
disease; studies
that compare two
groups: those who
have a specific
condition and those
who do not have
the condition15.2 Appraising the Evidence 407