Prof Clarke has 30 years experience in the rigourous evaluation of the effects of health and social care, including numerous randomised trials, systematic reviews and other prospective studies. He has been actively involved in the design, conduct, monitoring and reporting of dozens of randomised trials, including several that have recruited more than 1000 participants (in breast cancer, maternity care, poisoning and sub-arachnoid haemorrhage). He has provided detailed advice for hundreds of other trials, processed and interpreted the individual participant data (IPD) from more than a thousand trials included in systematic reviews, and assessed reports for tens of thousands more as part of initiatives to improve access to research information. His work on systematic reviews includes the collection of IPD from randomised trials across all treatments for women with breast cancer, leading to internationally-renowned reports that influence the care of millions of women worldwide.

Prof Clarke's research, coupled with more than two decades of teaching about randomised trials and systematic reviews (including establishing the relevant modules on the University of Oxford's MSc in Evidence Based Health Care) have provided him with unique insights into the evaluation of health and social care. He is building on this experience when designing and conducting research into research methodoogly, and established the SWAT and SWAR (Studies Within A Trial / Review) initiatives to facilitate this.

Prof Clarke is the Director of the Northern Ireland Clinical Trials Unit and the Northern Ireland Methodology Hub, and Co-ordinating Editor of the Cochrane Methodology Review Group. He has been a leading proponent of the importance of using systematic reviews in the design and reporting of clinical trials for some time, and his work on core outcome sets (as part of the COMET Initiative) also serves to improve the quality and usefulness of trials and reviews. His research reflects his strong interest in increasing the capacity for reviews and trials, and in improving their accessibility, in particular in low- and middle-income countries. He is Podcast Editor for the Cochrane Library and a founder of Evidence Aid, seeking to make it easier to use evidence from reviews in natural disasters and other humanitarian emergencies, and is the charity's Research Director and Chair of the Board of Trustees.