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Looking for grey literature can unearth the unpublished trials which show interventions in a less-than-glowing light and can significantly affect the outcome of a systematic review.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).

https://libguides.kcl.ac.uk/systematicreview/greylit (Kings College London)

If you are planning a Systematic Review or would like to search more systematically in your Research, the Research Support Librarian can help.

• Consultation to discuss your project
• Provide training/workshops to introduce researchers to the concept of Systematic Reviews
• Show researchers how to be systematic in their approach to research
• Collaborate in running scoping searches (sample search strings), to assess the viability of the research question for a systematic review across multiple databases
• Advise on which databases to use & how to search them systematically
• Advise on using a reference management tool to take out duplications as part of the screening process
• Advise on screening/review management tools such as Covidence, EPPI Reviewer, or Rayyan QCRI

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):
https://doi.org/10.1080/1364557032000119616 

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.

What is an Umbrella Review?

"With the increase in the number of systematic reviews available, a logical next step to provide decision makers in healthcare with the evidence they require has been the conduct of reviews of existing systematic reviews. Syntheses of existing systematic reviews are referred to by many different names, one of which is an umbrella review. An umbrella review allows the findings of reviews relevant to a review question to be compared and contrasted. An umbrella review's most characteristic feature is that this type of evidence synthesis only considers for inclusion the highest level of evidence, namely other systematic reviews and meta-analyses. " https://doi.org/10.1097/xeb.0000000000000055 

Its important to note that in these reviews, no primary studies are included just reviews. The quality of the reviews is assessed by assessing the methodologies of the reviews  and/or the methodologies of the primary studies.

"different people may have quite  different types of studies in mind when they use terms  such as “systematic literature review.” At a minimum, this range of understanding can result in confusion and unclear expectations and, in some cases, it could even impact the success of the literature review as a standalone project or the success of associated downstream  activities such as qualitative or quantitative research or external submissions."

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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.

source: https://libguides.rcsi.ie/systematicreviews#s-lg-box-14863443