- Posted By: Vicki Barber
Professor Jonathan Cook, Deputy Director of the Surgical Intervention Trials Unit (SITU), within OCTRU has recently had a number of papers published on this question. Read on to find out about Professor Cook's findings in his own words:
"The randomised controlled trial (RCT) is widely considered to be the gold standard study design for comparing the effectiveness of health interventions. A key aspect of the design of a RCT is a calculation of the number of participants needed (the sample size). This provides reassurance that the study will likely detect this difference (where it exists), with the required level of statistical precision. Determining an appropriate sample size by specifying the target difference is of crucial importance; too large or small and a study might be considered unethical, wasteful or lead to a potentially misleading conclusion. The sample size is typically involves specifying a target difference, the difference in the outcome of interest which is desired to be detected. One common approach is to specify a difference that is considered clinically important. Within medicine, various methods have been proposed to formally determine target differences, but their relative merits are unclear, and the availability and suitability of alternative methods from non-medical fields is unknown.
The DELTA (Differnce ELicitation in TriAls) project was a three part project which sought to assess available methods for specifying the target difference in RCT sample calculations. It was funded by the Medical Research Council and the National Institute for Health Research in the UK It was led by Jonathan Cook (http://www.ndorms.ox.ac.uk/profiles.php?profile=jcook) and Professor Luke Vale of Newcastle University and involved collaborators in the UK, Ireland and Canada. The project had three parts, i) a comprehensive systematic review of the medical and non-medical literature for methods which could be used, ii) two surveys of clinical trialists (1. The membership of the international Society for Clinical Trials; 2. UK and Ireland Clinical Trial Units, Trial Methodology Research Hubs and Research Design Service offices) and iii) development of guidance for researchers regarding specification of the target difference and the use of available methods.
Findings from the project have recently been published in leading journals:
http://www.journalslibrary.nihr.ac.uk/hta/volume-18/issue-28,
http://ctj.sagepub.com/content/11/3/300.full.pdf+html,
and http://www.plosmedicine.org/article/info%3Adoi%2F10.1371%2Fjournal.pmed.....
Seven methods for specifying the target difference are available; each with variation in its implementation and different advantages and disadvantages. While most trial groups in the UK and Ireland stated that they used a formal method to help determine the target difference in their most recent trial this does not appear to be fully reflected in trial protocol and publication. There is clear scope for better reporting of the target difference and use of methods to specify it. This would aid health professionals, patients, researchers and funders in judging the strength of the evidence and ensuring better use of scarce resources".