6 Evidence Appraisal: Research 99
Systematic Reviews
Systematic reviews summarize critically appraised research evidence (usually ex-
perimental and quasi-experimental studies) related to a specific question. Such re-
views employ and document comprehensive search strategies and rigorous, trans-
parent appraisal methods. Bias is minimized when a group of experts, rather than
individuals, applies standardized methods to the review process. The Institute
of Medicine (2011) appointed an expert committee to establish methodological
standards for developing and reporting of all types of systematic reviews.
The Agency for Healthcare Research and Quality (AHRQ) awards 5-year con-
tracts to North American institutions to serve as Evidence-based Practice Centers
(EPCs). EPCs review scientific literature on clinical, behavioral, organizational,
and financial topics to produce evidence reports and technology assessments
(EPC Evidence-Based Reports, 2016). Additionally, EPCs conduct research on
systematic review methodology. A systematic review is interchangeable with an
evidence report.
Systematic reviews use meta-analysis or meta-synthesis to analyze the combined
results of multiple research studies. Systematic reviews of quantitative studies are
referred to as meta-analyses. Meta-analysis provides a more precise estimate of
the effects of healthcare interventions than those derived from individual studies
included in the review by providing a common metric, which is called an effect
size (Polit & Beck, 2017). Through use of statistical methods, meta-analysis aids
in understanding not only the existence of a relationship between study variables
but also an estimate of the magnitude of the relationships across studies (Polit
& Beck, 2017). Meta-analyses that include only randomized controlled trials
(RCTs) are Level I evidence. Meta-analyses that contain quasi-experimental stud-
ies are categorized at a lower level of evidence.
When a systematic review summarizes the results of independent qualitative
studies, it is referred to as a meta-synthesis. Meta-synthesis combines the results
from a number of qualitative studies to arrive at a deeper understanding of the
phenomenon under review and produces a broader interpretation than can be
gained from a single qualitative study.
