A high-quality systematic review is designed to be the most reliable source of evidence to guide clinical practice. The purpose of a systematic review is to deliver a detailed summary of all the available primary research in response to a well constructed, specific research question.
Systematic reviews use existing research and are sometimes called ‘secondary research’ (research based on research). Today, systematic reviews are often required by funding agencies and institutions to establish a baseline of existing knowledge and are frequently used in healthcare guideline development.
In nursing, researchers may be interested in questions of systematic reviews about the effectiveness of interventions on patient outcomes. These types of reviews synthesize quantitative research via a meta-analysis (a statistical pooling of data extracted from primary research) or if meta-analysis is not possible, a narrative and tabular synthesis of extracted data. When meta-analysis is possible, the research can determine confidence intervals and judge the precision of the pooled result. In addition, the statistical procedures (eg odds ratios, weighted mean differences) weigh the contribution of individual studies so that low powered, imprecise studies contribute less to the bottom line than a high powered, precise study. Therefore, clinical decision-makers can have more confidence in the direction and magnitude of the findings because of the rigor and power of the pooled result.
In addition to the evidence about the effectiveness of interventions, nurses need to understand how patients experience their health, illness, symptoms and even the way that we deliver care. The richness of meaning of an experience cannot be extracted from a trial. Instead, qualitative evidence is more appropriate to address these kinds of questions. Systematic reviews of qualitative evidence synthesize narrative data by aggregating themes and findings from primary qualitative studies. These types of systematic reviews can help nurses understand patient values, preferences and experiences.
Systematic reviews are marked by transparency in methods and exhaustive approaches to searching. Therefore, the authors should identify the search strategy, sources (which should be many relevant databases and grey literature sources), key words and even the logic of the search. In addition, the authors should be very clear what types of studies they considered and what tools they used to judge the quality of the evidence. At least two researchers should have evaluated the studies for inclusion and verified the data extraction. If these elements of transparency are missing, it is difficult to judge the quality of the systematic review or if it is a systematic review at all.–Lisa Hopp PhD, RN