Home' Australian Pharmacist : Australian Pharmacist June 2013 Contents 64
Australian Pharmacist June 2013 I ©Pharmaceutical Society of Australia Ltd.
EVIDENCE BASED MEDICINE IN ACTION
outcome and may introduce researcher’s
bias in interpreting the outcomes.
Other problems include the possibility
of confounders and sampling bias,
whereby the subjects in the sample may
not be representative of all patients with
Clinical trials are interventional in nature,
in that the researcher intervenes by
manipulating the presence or absence of a
risk factor. Clinical trials are characterised by
a control group identical to the intervention
group in every way except for the exposure
to the intervention. Ideally, clinical trials
should be RCTs (described in the April issue
of Australian Pharmacist, page 71).
Quasi-experimental studies have some
features of an RCT but not all of them.
A quasi study might be the best approach
when it is not possible to undertake an
RCT. This may be because it is not possible
to randomise subjects or because it is not
possible to withhold treatment from one
group of participants. In a quasi-study,
random allocation is replaced by ‘matching’
in an attempt to achieve equivalence of
the groups. However, it is not possible to
say with much certainty that the outcome
was due to the intervention administered.
Hence these studies are generally
considered second best when determining
the evidence of effectiveness.
Another type of intervention studies
particularly used in the evaluation of service
initiatives, including pharmacy, is the
before-after design. It includes collection
of structured baseline data, prior to an
intervention, for variables on which the
intervention is expected to impact, followed
by data collection on one or more occasions
after the intervention. The before-and-after
data sets are then compared. A potential
problem with before-and-after studies
that does not include a control group is to
attribute changes to the intervention rather
than any other circumstance.
Descriptive studies are records of events
which include studies that look at
particular series of cases or cross-sections
of a population to look for particular
characteristics. They do not try to quantify
relationships but try to give us a picture
of what is happening in a population.
Descriptive studies include case
reports, case series and cross-sectional
Case reports and case series
Case reports describing individual patients
and case series describing treatment or
illness in small group of patients are often
the first description of a new disease,
symptom or treatment. Authors often
publish case reports to alert other health
care professionals about the therapy,
disease state or any other unusual and
rare conditions. Case studies are relatively
easy and cheap to conduct. If there are
any interesting cases or new presentations
then a case report can be easily written.
However, their weaknesses outweigh their
strengths. They do not provide explanations
and cannot show an association between
cause and effect. They also lack a control
group and hence the contributory cause
cannot be proven. But they may be useful
and often form the basis for future research
studies with stronger evidence designs on
the treatment or disease reported.
Cross-sectional studies are descriptive
studies that examine the relationship
between diseases and other variables of
interest as they exist in a defined population
at one particular time (i.e. exposure and
outcomes are measured at the same
time). They are best suited for quantifying
the prevalence of a disease or risk factor
and for quantifying the accuracy of a
diagnostic test. They are cheap and simple.
However, they do have disadvantages –
recall bias, confounders may be unequally
distributed, and group sizes may be
unequal. In addition, they may establish
association but not causality.
Editorials and expert opinion
The expertise or clinical judgement of a
healthcare professional occasionally plays a
role in EBM, especially when methodologically
sound research may not be available to answer
the clinical question. Both expert opinion as
well as research should be evaluated for biases.
Although most of the focus in this article
has been on quantitative research designs,
qualitative research does play an important
role in EBM. Qualitative research focuses
on how individuals or groups view and
understand their experiences. They are useful
for in-depth answers to questions that cannot
be answered numerically.
In conclusion, the study designs employed by
researchers are many and varied. The choice of
the study design employed usually depends
upon the study objectives and what is
workable in a practice setting. The design of
the study will suggest the potential biases you
can expect. It is critical that these limitations
in design are identified and considered by
health care practitioners when interpreting
• Centre for Evidence-Based Medicine:
• University of Illinois at Chicago.
Evidence-Based Practice in Health Sciences:
• Aveyard H, Sharp P. A beginner’s guide to
Evidence-Based Practice in health and social
care. McGraw Hill Education; 2011.
• Bryant PJ, Pace HA. The pharmacist’s guide
to Evidence-Based Medicine for clinical
decision making. American Society of
Health-System Pharmacists; 2009.
• Smith F. Research methods in pharmacy
practice. Pharmaceutical Press; 2002.
Figure 1: Levels of evidence
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