Cochrane Reviews are systematic reviews of research in health care and policy, and are internationally recognized as a high-quality source of evidence for decision-making. They collate and summarize all the best available research evidence on the effects of healthcare interventions or the accuracy of diagnostic tests into a systematic review.

Outcome selection data in systematic reviews needs to be relevant to patients, clinicians and policy-makers if the findings of a review are to influence practice and future research. Missing data, or inconsistent reporting of outcome data, in clinical research can negatively affect the quality of evidence within a systematic review. A potential solution is an agreed standardized set of outcomes known as a core outcome set (COS). These represent the minimum that should be measured and reported in all clinical trials of a specific condition, and are also suitable for use in clinical audit or research other than randomized trials.
 
Among its many international collaborators, Cochrane is working with the COMET (Core Outcome Measures in Effectiveness Trials) Initiative, which brings together people interested in the core outcome sets.

We spoke with Hywel Williams (Cochrane Skin), Anne-Marie Glenny (Cochrane Oral Health) and Jochen Schmitt (Cochrane Skin) about their involvement with COMET, core outcome set development and the opportunities for Cochrane to engage in this work. 

All three Cochrane contributors emphasize the importance of core outcome sets (COS) for review production. 

‘For me, the lack of common outcomes that are valid and meaningful to health care professionals and patients are one the most important obstacles for preventing any sensible form of comparison between different studies of skin diseases’, says Hywel Williams. ‘The lack of pooled analysis or pooling of very different outcomes in a desperate attempt to make some form of summative comparisons will continue until core outcomes for clinical trials are developed and used.’
Anne-Marie Glenny adds: ‘We have many reviews with a vast number of differing outcomes that mean no pooling of data is possible. We hope that developing COS will encourage trialists to focus on common, patient-focused outcomes and reduce research waste.’
 
The work of COMET in the COS environment is very important. COMET provides a searchable database, a networking facility, and a resource for methodological advice. Cochrane Skin has made the development of core outcome sets a priority, and has set up an international collaboration called the Cochrane Skin Group Core Outcome Set Initiative (CSG-COUSIN). In oral health, there is such a diverse range of outcome measures across reviews (including pain, gingivitis, mortality, caries, mucositis) that it is beyond the Group’s capacity to develop COS for all relevant areas. However, support is provided to review authors if this is something they wish to pursue. 

Jochen Schmitt refers to the importance of cooperation among reviewers, trialists, and methodologists to resolve the current problems of "outcome heterogeneity". He continues explaining why he feels Cochrane Review Groups (CRGs) could play a key role in this: ‘They are widely accepted, globally acting, and the COS topic is really central for the Cochrane mission to become the leading advocate for evidence-informed healthcare. Since the establishment of CSG-COUSIN the annual Skin Group meeting always spends half a day on COS.’ 

So what is it that CRGs can do to strengthen COS development? The inclusion of the topic in Group meetings is a very practical suggestion and will stimulate thinking and reflection about COS development in the Group’s thematic area of work. Hywel Williams says: ‘Most systematic reviewers spend a lot of time thinking about their outcomes, so it is natural that many will want to become involved in collaborative initiatives that develop core outcomes. At Cochrane Skin, we point potential review teams to existing core outcome set initiatives in skin at title registration form stage, and encourage our reviewers to have a dialogue with those developing core outcome sets.’ But Anne-Marie Glenny acknowledges, ‘The time it takes to get involved may be an obstacle for authors to engage. We should identify priority areas where COS would really be beneficial, which is not necessarily the case for all reviews. We need to think carefully about resources required before embarking and about how the resulting COS will be incorporated into updating/ongoing reviews.’

In addition to the work of COMET, Jochen Schmitt emphasizes the importance of discipline specific COS-groups because of the need for specific clinical expertise and a detailed understanding of clinical trials and review issues necessary for appropriate COS development and their implementation. It is also essential to prevent the development of more than one COS for one indication, a situation already happening in pain therapy, thus adding to outcome heterogeneity rather than resolving it. Jochen Schmitt also points to another challenge: ‘COMET is primarily dedicated to develop core outcome domain sets. This is an important first step, but the selection of the best core outcome measurement instrument is essential to make COS really meaningful.’ 
 
So what does this all mean for Cochrane reviewers? This is well summarized by the following statement from Hywel Williams: ‘If, like Cochrane Skin, your review outcomes are all over the shop and plagued with a multitude of unvalidated and clinically meaningless outcomes that prevent pooling of trials, then tackle the problem head on by developing a collaboration with those interested in, and who have methodological expertise in developing core outcome sets.’

About COMET
COMET brings together people interested in the development and application of agreed standardized sets of outcomes (core outcome sets). COMET aims to collate and stimulate relevant resources, both applied and methodological, to facilitate exchange of ideas and information, and to foster methodological research in this area. This is being achieved through:

• Development of a searchable database of completed and ongoing projects in core outcome set development;
• Development of a repository for project protocols and other documents (such as questionnaires), with the intention that this will be searchable;
• Maintenance of these resources in a publicly available searchable database;
• Preparing guidance on developing and reporting core outcome sets;
• Preparing guidance on integrating patient reported outcomes into core outcome sets; and
• Guidance on obtaining funding to develop core outcome sets.

For more information, please contact:
Hywel Williams: Hywel.Williams@nottingham.ac.uk
Anne-Marie Glenny: cochraneoralhealth@manchester.ac.uk
Jochen Schmitt: Jochen.Schmitt@uniklinikum-dresden.de