Clinical Trials

❘❙❚■ Chapter 8 | BlindingBlinding or masking?In clinical trials, the term ‘blinding’ has been defined as an experimentalmethodology in which groups of individuals involved in a trial are made unawareof which treatment the participants are assigned to. The term blinding has beenchallenged because it should be reserved to describe visual impairment. The term‘masking’ is therefore used by some research organizations such as the USNational Institutes of Health. Terms such as single blind and double blind are stillingrained in trial terminology, making it hard to replace them completely.Here, we will use the term blinding, so as to be able to appreciate the olderdefinitions, although we would encourage the use of masking otherwise.Why do we need blinding in studies?Most human beings have opinions and preconceptions. When these opinions areunsubstantiated by evidence, individuals can be said to be biased. In a trial,knowledge of which treatment a patient is assigned to can lead to subjective andjudgmental bias by the patients and investigators. This bias can influence thereporting, evaluation, and management of data and can distort statistical analysisof the treatment effect [1,2]. In practical terms, it is extremely difficult toquantitatively assess such bias and its impact on the evaluation of treatment effect.Bias can occur in clinical trials because, generally, patients wish to be given thelatest new treatments and doctors hope to be involved in a study that will succeed.Both patients and doctors want the effects of a new treatment to be more favorable,which can result in the underreporting of side-effects. It is therefore critical toneutralize such bias by masking the identity of treatments so that trial participantsare blinded to the nature of the treatment.At each stage of a trial, there are a variety of individuals who can introduce bias.These individuals include patients, principal investigators, physicians, surgeons,sponsors, and other healthcare professionals, local study coordinators (who mayalso be principal investigators themselves), core labs reporting on scans or bloodsamples, trial statisticians, and committees such as the adjudication or datamonitoring and safety committee (DMSC). Therefore, each of these groups canbe blinded.76