Double-blind study: features and advantages of this design

A double-blind study is an experimental method used to ensure impartiality and avoid errors derived from the bias of the participants and the researchers themselves.

While “classic” studies with a control group and experimental group work, they are not as safe as double-blind studies, in which even researchers do not know who they are administering the experimental treatment to.

Below, we’ll take a look at how these types of studies work, along with a review of the concept of the placebo effect, its importance in research, and how it’s controlled.

    What is a double blind study?

    Double blind studies are a type of scientific research used to prevent research results from being influenced by the placebo effect, Arising from research participants and the observer effect, caused by the researchers themselves. These studies are very important in many fields of research, especially in health sciences and social sciences.

    The main aspect of double-blind studies is that participants and researchers they do not know at first which subjects are part of the experimental group and which subjects are part of the control group.

    Thus, researchers do not know which participants are receiving the treatment or condition they want to know what effects it has, nor do they know which participants are receiving a condition with no effect (placebo).

    Blind studies

    In scientific research, blind studies are very important tools that allow avoid bias related to participants’ perception of the experimental treatment they are receiving. It is important to understand this type of study before going into the detail of double blind studies, and for this reason to speak at length about how blind studies are.

    To better understand how blind studies work, we are going to put a hypothetical pharmaceutical investigation case, in which we want to verify the effectiveness of a drug, in particular an antidepressant. We do not know what the positive and negative effects of this drug are on health, but it is expected to help improve mood in people with depression.

    100 volunteers suffering from depression are presented to the study. Since we want to know the real effectiveness of this drug, we separate these 100 participants into two groups of 50 people each. One will be the experimental group, which will receive the antidepressant, while the other will be the control group, which will receive a pill identical to the antidepressant in appearance, but which is in fact a placebo, i.e. say a substance with no effect on health.

    The reason half of the participants do not receive an antidepressant is primarily to prevent the placebo effect from skewing research results. The placebo effect occurs when a person, unconsciously, he notices an improvement because he has been told that the treatment he received has therapeutic power. It may not cure anything, but as the person wishes, they begin to notice improvements that are not real.

    When creating a control group and an experimental group, it is easier to know how much the actual drug exerts changes, and what changes in particular. Any improvement observed in the experimental group that is not observed in the control group will be attributed to the therapeutic power of the investigational drug. In blinded studies, no participant knows whether they received the drug or the placebo, so there is less chance of sham improvements, which is the main advantage of this type of study.

    The problem with this type of study is that researchers know which participants are getting the actual treatment and which are getting the placebo treatment. It may seem obvious and necessary, but it is also a source of bias. Researchers may think they see significant improvements in the experimental group that do not actually exist (observer effect)

    In addition, it may be that when randomizing participants, and passing some to the control group and others to the experimental, the researchers themselves may decide to consciously include some patients because they believe that ‘they have many possibilities to improve the experimental treatment. . This is not entirely ethical, because in this case the results would be “inflated”.

      Double-blind studies in more depth

      Fortunately, to overcome the limitation of blind studies double blind studies exist. To avoid the bias attributed to the placebo effect and also the bias attributed to the observer effect, participants and researchers do not know who makes up the control group and who makes up the experimental group. Because researchers don’t know which participants are getting an experimental treatment, they can’t attribute improvements to it until they statistically analyze the data.

      The vast majority of researchers are professionals, there is no doubt about it. however, there is always the possibility that the researcher will unconsciously alert the participant to the treatment they are receiving, Showing you which group you belong to. You can even play favoritism by giving treatment to patients who think they have a better response, as we have already mentioned.

      Because neither the experimenters nor the participants know who is receiving the treatment, the highest level of scientific rigor is achieved. The only ones who know who is in each group are third parties, who have devised a coding system that will ensure that each participant receives treatment or not and without the experimenters knowing what they are giving. Researchers will know which people gave them the treatment when, during the study of the data, the codes of each participant are revealed to them.

      Coming back to the case of the pharmaceutical study, in this case we would have a pill that would be the real medicine and another pill that would be a placebo, looking the same. Each participant would have received a special code, codes that the researchers would know but would not know what they mean, they would only know that, for example, participant number 001 should receive the pill which is in a box with the number 001, and so on with the 100 subjects in the experiment, assuming that 50 will receive treatment and 50 will receive a placebo.

      After each participant has received the pills, the time stipulated in the experiment is allowed to elapse. Once the experience is successful and the data of each patient collected, they will have reported the changes they have observed, their physiological state and other measures, these data will be statistically analyzed. It is at this point that the people who designed the coding system inform the experimenters who received the treatment and those who did not. In this way, empirical evidence can be obtained as to whether the treatment is working or not.

      Bibliographical references:

      • Hróbjartsson, A; Emanuelsson, F; Skou Thomsen, AS; Hilden, J; Brorson, S (2014). “Bias due to lack of blinding of patients in clinical trials. A systematic review of randomized trials of patients in blind and non-blind sub-studies.” International Journal of Epidemiology. 43 (4): 1272–83. doi: 10.1093 / ije / dyu115. PMC 4258786. PMID 24881045
      • Bello, S .; Moustgaard, H .; Hróbjartsson, A. (2014). “The risk of outcome has been reported infrequently and incompletely in 300 publications of randomized clinical trials.” Journal of Clinical Epidemiology. 67 (10): 1059-1069. doi: 10.1016 / j.jclinepi.2014.05.007. ISSN 1878-5921. PMID 24973822

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