The key features of a systematic review or systematic research synthesis are that:
(Source: EPPI (Evidence Informed Policy & Practice) Centre)
Publication bias refers to the fact that studies with more ‘positive’ results – i.e. which show a definite effect for a particular treatment – are more likely (three times more likely in fact) to be published than ones which show little or no positive effect for a treatment.
Researchers themselves often think that studies which show no or little effect for a treatment aren’t worth publishing so these studies are less likely to be submitted for publication – the so-called ‘file-drawer’ problem. Once submitted they are less likely to be accepted by a journal, less likely to be published in a ‘high-impact’ journal and less likely to be published in English making them all the more difficult to find.
Less scrupulous researchers are sometimes known to selectively report the results of trials, reporting results that show treatments in a good light while glossing over ones which show that it is ineffective in a process called HARKing – Hypothesizing After the Results are Known.
Looking for grey literature can unearth the unpublished trials which show interventions in a less-than-glowing light and can significantly affect the outcome of a systematic review. A good example of this is this study into the anti-depressant Agomelatine (see the box on this page).
If you are planning a Systematic Review or would like to search more systematically in your Research, the Research Support Librarian can help.
Systematic reviews can be broadly defined as a type of research synthesis that are conducted by review groups with specialized skills, who set out to identify and retrieve international evidence that is relevant to a particular question or questions and to appraise and synthesize the results of this search to inform practice, policy and in some cases, further research. The Cochrane Database of Systematic Reviews is the global repository of such systematic reviews.
Scoping reviews determine the scope or coverage of a body of literature on a given topic and give clear indication of the volume of literature and studies available as well as an overview (broad or detailed) of its focus. Scoping reviews are useful for examining emerging evidence when it is still unclear what other, more specific questions can be posed and valuably addressed by a more precise systematic review
Munn, Z., Peters, M.D.J., Stern, C. et al. Systematic review or scoping review? Guidance for authors when choosing between a systematic or scoping review approach. BMC Med Res Methodol 18, 143 (2018). https://doi.org/10.1186/s12874-018-0611-x
Hilary Arksey & Lisa O'Malley (2005) Scoping studies: towards a
methodological framework, International Journal of Social Research Methodology, 8:1, 19-32, (2005):
Sometimes while a Systematic Review is requested, what may be needed is conducting the Literature Review in a more structured or systematic manner. This involves identifying the best resources to search, planning out the search steps and searching them in the best way. These are often smaller scale projects conducted by an individual. The Research Support Librarian can advise you on this.
Rapid reviews target high quality and authoritative resources for time-critical decision-making or clinically urgent questions.
Like a systematic reviews they aim to identify the key concepts, theories and resources in a field, and to survey the major research studies. Less time may be spent on critical appraisal as systematic reviews, evidence briefs and clinical guidelines are sought in preference to exhaustive coverage of primary studies. The objective is to apply systematic levels of search and appraisal but within shorter timeframes.