Most Cochrane Reviews focus tightly on an intervention or class of interventions for a specific condition or in a particular population or setting. As a result, readers of The Cochrane Library may need to consult several related Cochrane Reviews to find the evidence they need. Cochrane Overviews were designed to address this problem by providing a “friendly front end” to The Cochrane Library - with the expectation that Overview readers would use them to discover the presence of a set of related reviews in the library, and to get an idea of the contents of these reviews, with the option of going to the individual reviews if they wished additional detail.
The Overviews published to date have shown a wide variation in their scope, content and methods. Most have included only Cochrane Reviews, but a few have extended their search to systematic reviews published elsewhere. The number of reviews included in each Overview ranges from 3 to 54. Overview authors have also taken different approaches to the synthesis of data from included reviews.
In some cases, it has been possible to rank interventions by their effectiveness or adverse effects using network meta-analysis. This recently developed method allows Overview authors to make "indirect comparisons" between interventions for which no direct head-to-head trials have been found, and to include both the direct and indirect comparisons in their analyses. A key assumption underlying network meta-analysis is that the trials included in the analysis bear sufficient similarity to one another to make indirect comparisons appropriate. This has been labelled the "transitivity assumption" or "similarity assumption" and requires that the included trials should, at least in theory, be "jointly randomisable" - that is, that a subject in any one of the trials included in the network could have, in principle been assigned to any one of the other interventions being compared. More information about Network Meta-Analysis and its assumptions is available on the website of the Cochrane Comparing Multiple Interventions Methods Group (cmimg.cochrane.org). Four of the currently published Cochrane Overviews have taken this approach and present new analyses of the data from trials included in the Cochrane Reviews that they cover.
In the majority of cases, Overview authors have not been able to ensure that the transitivity assumption is satisfied, and have not attempted to rank interventions or to perform new analyses. Many of these Overviews include tables that juxtapose results of direct comparison meta-analyses performed in a number of related reviews to allow readers more easy access to this body of related evidence. While it may be tempting for the reader to try to rank interventions or do "informal" indirect comparisons using these tables, this temptation should be resisted. The transitivity assumption is equally important in this setting, and these informal indirect comparisons can lead to inaccurate conclusions if there were significant differences between the trials included in the different systematic reviews that contributed data to the table.
A minority of Overviews do not attempt to provide either direct or indirect comparisons. Overviews of this sort tend to deal with complex interventions where specific components may vary across trials. The authors use the results of the included reviews to provide a map of the existing evidence, often providing their own taxonomy of interventions or outcomes.
The Cochrane Overviews included in this special collection have been prepared by authors and editors from a diverse range of Cochrane Review Groups including the Cochrane Musculoskeletal Group, Cochrane Airways Group, Cochrane Tobacco Addiction Group, Cochrane Menstrual Disorders and Subfertility Group, Cochrane Hepato-Biliary Group, Cochrane Pain, Palliative and Supportive Care Group, Cochrane Drugs and Alcohol Group, Cochrane Effective Practice and Organisation of Care Group, Cochrane Consumers and Communication Group and Cochrane Pregnancy and Childbirth Group.
1. Cipriani A, Higgins JPT, Geddes JR, Salanti G. Conceptual and Technical Challenges in Network Meta-analysis. Ann Intern Med 2013 Jul;159(2):130-137. dx.doi.org/ 10.7326/0003-4819-159-2-201307160-00008
2. Salanti G. Indirect and mixed-treatment comparison, network, or multiple-treatments meta-analysis: many names, many benefits, many concerns for the next generation evidence synthesis tool. ResSynthMeth 2012;3(2):80–97. dx.doi.org/ 10.1002/jrsm.1037
Acknowledgements: With thanks to Lorne Becker for drafting the introduction text, arranging the Overviews for this collection, and for comments and edits.
Biologics for rheumatoid arthritis: an Overview of Cochrane reviews
The biologic disease-modifying anti-rheumatic drugs (DMARDs) are very effective in treating rheumatoid arthritis (RA), however there is a lack of head-to-head comparison studies. This Overview aims to compare the efficacy and safety of abatacept, adalimumab, anakinra, etanercept, infliximab, and rituximab in patients with RA.
Adverse effects of biologics: a network meta-analysis and Cochrane Overview
Biologics are used for the treatment of rheumatoid arthritis and many other conditions. While the efficacy of biologics has been established, there is uncertainty regarding the adverse effects of this treatment. Important risks such as lymphomas, serious infections and tuberculosis (TB) reactivation may be more common to the biologics but occur in small numbers across the various indications. This Overview aims to compare the potential adverse effects of tumor necrosis factor inhibitor (adalimumab, certolizumab, etanercept, golimumab, infliximab), interleukin (IL)-1 antagonist (anakinra), IL-6 antagonist (tocilizumab), anti-CD28 (abatacept), and anti-B cell (rituximab) therapy in patients with any disease condition except human immunodeficiency disease (HIV/AIDS).
Safety of regular formoterol or salmeterol in children with asthma: an Overview of Cochrane reviews
Two large surveillance studies in adults with asthma have found an increased risk of asthma-related mortality in those who took regular salmeterol as monotherapy in comparison to placebo or regular salbutamol. No similar sized surveillance studies have been carried out in children with asthma, and we remain uncertain about the comparative safety of regular combination therapy with either formoterol or salmeterol in children with asthma. This Overview aims to use the paediatric trial results from Cochrane Systematic Reviews to assess the safety of regular formoterol or salmeterol, either as monotherapy or as combination therapy, in children with asthma.
Pharmacological interventions for smoking cessation: an Overview and network meta-analysis
Smoking is the leading preventable cause of illness and premature death worldwide. Some medications have been proven to help people to quit, with three licensed for this purpose in Europe and the USA: nicotine replacement therapy (NRT), bupropion, and varenicline. Cytisine (a treatment pharmacologically similar to varenicline) is also licensed for use in Russia and some of the former socialist economy countries. Other therapies, including nortriptyline, have also been tested for effectiveness. This Overview aims to address the following questions: How do NRT, bupropion and varenicline compare with placebo and with each other in achieving long-term abstinence (six months or longer)? How do the remaining treatments compare with placebo in achieving long-term abstinence? How do the risks of adverse and serious adverse events compare between the treatments, and are there instances where the harms may outweigh the benefits?
Assisted reproductive technology: an Overview of Cochrane Reviews
As many as one in six couples will encounter problems with fertility, defined as failure to achieve a clinical pregnancy after regular intercourse for 12 months. Increasingly, couples are turning to assisted reproductive technology (ART) for help with conceiving and ultimately giving birth to a healthy live baby of their own. Fertility treatments are complex, and each ART cycle consists of several steps. If one of the steps is incorrectly applied, the stakes are high as conception may not occur. With this in mind, it is important that each step of the ART cycle is supported by good evidence from well-designed studies. This Overview aims to summarise the evidence from Cochrane systematic reviews on procedures and treatment options available to couples with subfertility undergoing ART.
Open, small-incision, or laparoscopic cholecystectomy for patients with symptomatic cholecystolithiasis. An Overview of Cochrane Hepato-Biliary Group reviews
Patients with symptomatic cholecystolithiasis are treated by three different techniques of cholecystectomy: open, small-incision, or laparoscopic. This Overview aims to summarise Cochrane Reviews that assess the effects of different techniques of cholecystectomy for patients with symptomatic cholecystolithiasis.
Single dose oral analgesics for acute postoperative pain in adults
Thirty-five Cochrane Reviews of randomised trials testing the analgesic efficacy of individual drug interventions in acute postoperative pain have been published. This Overview aims to summarise data from all Cochrane Reviews that have assessed the effects of pharmaceutical interventions for acute pain in adults with at least moderate pain following surgery, who have been given a single dose of oral analgesic taken alone.
Efficacy and safety of pharmacological interventions for the treatment of the Alcohol Withdrawal Syndrome
Alcohol abuse and dependence represents a very serious health problem worldwide with major social, interpersonal and legal interpolations. Pharmacological treatments presently used are of uncertain effectiveness and there is even more doubt on the comparative effects and value for money. This Overview aims to summarise Cochrane Reviews that assess the effectiveness and safety of pharmacological interventions in the treatment of alcohol withdrawal.
Antiepileptic drugs for neuropathic pain and fibromyalgia - an Overview of Cochrane reviews
Antiepileptic drugs have been used for treating different types of neuropathic pain, and sometimes fibromyalgia. Our understanding of quality standards in chronic pain trials has improved to include new sources of potential bias. Individual Cochrane Reviews using these new standards have assessed individual antiepileptic drugs. An early review from this group, originally published in 1998, was titled 'Anticonvulsants for acute and chronic pain'. This current Overview now covers the neuropathic pain aspect of that original review, which was withdrawn in 2009. It aims to provide an Overview of the relative analgesic efficacy of antiepileptic drugs that have been compared with placebo in neuropathic pain and fibromyalgia, and to report on adverse events associated with their use.
Interventions for treating pain and disability in adults with complex regional pain syndrome- an Overview of systematic reviews
There is currently no strong consensus regarding the optimal management of complex regional pain syndrome although a multitude of interventions have been described and are commonly used. This Overview aims to summarise the evidence from Cochrane and non-Cochrane Systematic Reviews of the effectiveness of any therapeutic intervention used to reduce pain, disability or both in adults with complex regional pain syndrome.
Neuraxial blockade for the prevention of postoperative mortality and major morbidity: an Overview of Cochrane systematic reviews
Various beneficial effects derived from neuraxial blocks have been reported. However, it is unclear whether these effects influence perioperative mortality and major pulmonary or cardiovascular complications. This Overview aims to summarise Cochrane Systematic Reviews that assess the effects of neuraxial blockade on perioperative rates of death, chest infection and myocardial infarction. A secondary objective is to summarise the evidence on adverse effects of neuraxial blockade.
Consumer-oriented interventions for evidence-based prescribing and medicines use: an Overview of systematic reviews
Numerous systematic reviews exist on interventions to improve consumers’ medicines use, but this research is distributed across diseases, populations and settings. The scope and focus of reviews on consumers’ medicines use also varies widely. Such differences create challenges for decision makers seeking review-level evidence to inform decisions about medicines use. This Overview aims to synthesise the evidence from systematic reviews on the effects of interventions which target healthcare consumers to promote evidence-based prescribing for, and medicines use, by consumers.
Pain management for women in labour: an Overview of systematic reviews
The pain that women experience during labour is affected by multiple physiological and psychosocial factors and its intensity can vary greatly. Most women in labour require pain relief. Pain management strategies include non-pharmacological interventions (that aim to help women cope with pain in labour) and pharmacological interventions (that aim to relieve the pain of labour). This Overview aims to summarise the evidence from Cochrane Systematic Reviews on the efficacy and safety of non-pharmacological and pharmacological interventions to manage pain in labour. The authors consider findings from non-Cochrane systematic reviews if there was no relevant Cochrane review.
An Overview of reviews evaluating the effectiveness of financial incentives in changing healthcare professional behaviours and patient outcomes
There is considerable interest in the effectiveness of financial incentives in the delivery of health care. Incentives may be used in an attempt to increase the use of evidence-based treatments among healthcare professionals or to stimulate health professionals to change their clinical behaviour with respect to preventive, diagnostic and treatment decisions, or both. Financial incentives are an extrinsic source of motivation and exist when an individual can expect a monetary transfer which is made conditional on acting in a particular way. There are numerous reviews performed within the healthcare area describing the effects of various types of financial incentives. The authors aim to conduct an Overview of systematic reviews that evaluates the impact of financial incentives on healthcare professional behaviour and patient outcomes.
Interventions for fatigue and weight loss in adults with advanced progressive illness
Fatigue and unintentional weight loss are two of the commonest symptoms experienced by people with advanced progressive illness. Appropriate interventions may bring considerable improvements in function and quality of life to seriously ill people and their families, reducing physical, psychological and spiritual distress. This Overview aims to summarise the evidence available within Cochrane Reviews on the efficacy of interventions used in the management of fatigue and/or unintentional weight loss in adults with advanced progressive illness.
Image credit: MONTY RAKUSEN/CULTURA/SCIENCE PHOTO LIBRARY, F007/0795
Date published: 29 January 2014
Contact: Cochrane Editorial Unit (firstname.lastname@example.org)