A clinical trial design in which neither the participants nor investigators know which participants are receiving the experimental medicine and which are receiving a
placebo (or comparator therapy). Double-blind trials are thought to produce objective results, since the expectations of the investigator and the participant do not affect the outcome. Also called double-masked
trial. In trials in studies comparing two active compounds (test medicine and comparator) and when
the two treatments cannot be made identical, double dummy is a technique for retaining the blind. Supplies are prepared for Treatment A (active and indistinguishable placebo) and for Treatment B (active and indistinguishable
placebo). Participants then take two sets of treatment; either A (active) and B (placebo), or A
(placebo) and B (active). For example, if we want to compare two medicines, one presented as green tablets and one as pink capsules, we could also supply green placebo tablets and pink
placebo capsules so that both groups of patients would take one green tablet and one pink capsule. Home » FAQ » What Is The Difference Between Single Blind And Double Blind Clinical Trials? When undertaking a clinical trial, the two major models that one can use are the single blind and double blind trials. Selecting the right trial is important since it can affect the
outcome of the trial or introduce errors. The ideal model should be selected based on the type of trial and other variables. For any clinical trial, there are usually two groups of people who are experimented on. Members of one group are given a placebo, and the members of another group are given the treatment that is being studied. This is so as to compare the effectiveness of the treatment to placebo. In a single blind study, the participants in the clinical trial do not know if they are
receiving the placebo or the real treatment. This is done to reduce the risk of errors, since some participants might produce spurious results if they know that they are taking the placebo or medication. In this model, the experimenter monitoring the participants knows which individuals received the placebo and which ones got the treatment under examination. In a double-blind study, both the participants and the experimenters do not know which group got the placebo and which got the
experimental treatment. This is considered to be the superior model of clinical research since it eliminates outcomes that are produced due to placebo effect, as well as observer bias by the experimenter. The fact that the experimenter does not know which group received the placebo or the experimental drug means that the risk of conscious and unconscious observer bias is reduced, making the study more accurate. NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-.  Definition/IntroductionA clinical research study or a clinical trial is an experiment or observation performed on human subjects to generate data on the safety and efficacy of various biomedical and behavioral interventions.[1] Blinding or masking refers to the withholding of information regarding treatment allocation from one or more participants in a clinical research study. It is an essential methodological feature of clinical studies that help maximize the validity of the research results.[2] Issues of ConcernBlinding covers any of the numerous participants of the clinical trial, e.g., researchers, subjects, technicians, and data analysts. Single-, double-, and triple-blinding are commonly used blinding strategies in clinical research. A single-blind study masks the subjects from knowing which study treatment, if any, they are receiving. A double-blind study blinds both the subjects as well as the researchers to the treatment allocation. Triple-blinding involves withholding this information from the patients, researchers, as well as data analysts.Randomized, double-blind placebo-controlled trials involve the random placement of participants into two groups; an experimental group that receives the investigational treatment and a control group that acquires a placebo. Neither the researchers nor the study subjects know who is getting the experimental treatment and who is getting a placebo. This type of clinical study ranks as the gold standard for the validation of treatment interventions.[3] Unfortunately, blinding is not possible to achieve in all clinical trials. For example, the method of drug delivery may not be amenable to blinding. An excellent clinical protocol may help ensure that within the ethical and practical constraints, blinding is achieved as effectively as possible. Clinical SignificanceBias refers to a deviation from the truth in the collection, analysis, interpretation, or publication of data, leading to false conclusions. Poor blinding of a clinical research study may lead to bias that may result in inflated effect size and increase the risk of type I error. Even a small error in blinding may lead to a statistically significant result without any real difference between the study groups.[4] Keeping both the researchers and the subjects blinded to treatment allows a double-blinded study to prevent the researchers from treating the study groups differently. The double-blinded study minimizes the risk of various types of biases, such as observer bias or confirmation bias, which may influence the results of the investigation.[5][6] It may also help avoid a disproportionately large placebo effect in the patients involved in the study.[3] Unblinding may occur during any portion of the blinded clinical trial. Unblinding that occurs before the conclusion of a trial may be a source of bias that the study should document and report. It is the responsibility of all the healthcare professionals involved in a clinical trial, such as physicians, nurses, pharmacists, technicians, and data analysts, to maintain blinding as effectively as possible during the trial and to report any premature unblinding.[7] Review QuestionsReferences1.Ranganathan P, Aggarwal R. Study designs: Part 1 - An overview and classification. Perspect Clin Res. 2018 Oct-Dec;9(4):184-186. [PMC free article: PMC6176693] [PubMed: 30319950] 2.Munnangi S, Sundjaja JH, Singh K, Dua A, Angus LD. StatPearls [Internet]. StatPearls Publishing; Treasure Island (FL): Aug 23, 2021. Placebo Effect. [PubMed: 30020668] 3.Probst P, Zaschke S, Heger P, Harnoss JC, Hüttner FJ, Mihaljevic AL, Knebel P, Diener MK. Evidence-based recommendations for blinding in surgical trials. Langenbecks Arch Surg. 2019 May;404(3):273-284. [PubMed: 30824993] Chen L, Su Y, Quan L, Zhang Y, Du L. Clinical Trials Focusing on Drug Control and Prevention of Ventilator-Associated Pneumonia: A Comprehensive Analysis of Trials Registered on ClinicalTrials.gov. Front Pharmacol. 2018;9:1574. [PMC free article: PMC6399618] [PubMed: 30863312] 5.Platt RW, Platt R, Brown JS, Henry DA, Klungel OH, Suissa S. How pharmacoepidemiology networks can manage distributed analyses to improve replicability and transparency and minimize bias. Pharmacoepidemiol Drug Saf. 2019 Jan 15; [PubMed: 30648307] 6.Clifton L, Clifton DA. How to maintain the maximal level of blinding in randomisation for a placebo-controlled drug trial. Contemp Clin Trials Commun. 2019 Jun;14:100356. [PMC free article: PMC6462539] [PubMed: 31011659] Copyright © 2022, StatPearls Publishing LLC. This book is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits use, duplication, adaptation, distribution, and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, a link is provided to the Creative Commons license, and any changes made are indicated. Bookshelf ID: NBK546641PMID: 31536248 ViewsIn this PageBulk DownloadRelated information
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See reviews...See all... Recent ActivityWho knows in doubleA type of clinical trial in which neither the participants nor the researcher knows which treatment or intervention participants are receiving until the clinical trial is over.
WHO is aware of which participants are receiving treatment in both single blind and doubleChapter 2. Does doubleDouble-blind trials are seen as the most reliable type of study because they involve neither the participant nor the doctor knowing who has received what treatment. The aim of this is to minimize the placebo effect and minimize bias.
Why is a placebo used in a doubleA placebo is an inactive substance that looks like the drug or treatment being tested. Comparing results from the two groups suggests whether changes in the test group result from the treatment or occur by chance.
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In a double-blind study, who knows which participants are getting the treatment or placebo?
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