Manipal Journal of Nursing and Health Sciences


Randomized Controlled Trial (RCT) is a classical research design, in which the participants are randomly allocated to one or other treatment conditions under the study. Researchers widely use randomized trials to evaluate the effectiveness of various pharmacological and non-pharmacological interventions. At the outset, randomization minimizes the bias in allocating subjects to the intervention and control group. However, it does not exclude the chances of differential treatment of groups or biased adjudication of outcome variables. Blinding helps in controlling various types of biases that might inadvertently sweep into the study. The two major biases that can be controlled using blinding are the performance bias and the ascertainment bias. The four groups of people blinded in the trial are the study subjects, the research investigator/s, the outcome assessor/s, and the data analyst/s. Based on the number of people blinded, trials are classified as open label trial, single blinded trial, double blinded trial, triple blinded trial, and quadruple blinded trial. Sometimes, it may be difficult or nearly impossible to do blinding because of methodological, technical, or ethical reasons. Researchers must ensure transparency in reporting the blinding. If, blinding was employed, mentioning the study as ‘double blinded’ or ‘triple blinded’ may not be sufficient. The researchers must explicitly report, which all individuals were blinded and how. Blinded RCTs can minimize bias to a greater extent. Blinding helps in prevention of biased ascertainment of outcomes and reduce the chance of co-interventions. Researchers must strive to blind as many individuals as practically feasible to limit the bias in RCTs

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