Double-blind study: characteristics and advantages of this design

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

Although the "classical" studies with control group and experimental group work, they are not as safe as the double-blind, in which not even the researchers themselves know who they are giving the experimental treatment to.

Below we will see in depth how these types of studies work, in addition to reviewing the concept of the placebo effect, its importance in research and how it is controlled.

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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, caused by the research participants, and the observer effect, caused by the researchers themselves. These types of studies are very important in many research fields, especially in health sciences and social sciences.

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

Thus, the researchers do not know which participants are receiving the treatment or condition being they want to know what effects it has and they also don't know which participants receive a condition with no effect (placebo).

blind studies

In scientific research, blind studies are very important tools that allow avoid biases related to the perception of the participants regarding the experimental treatment they receive. It is important to understand these types of studies before going into detail about double-blind studies, and for this reason to talk at length about what blind studies are like.

To better understand how blind studies work, we are going to present a hypothetical case of a pharmaceutical research, in which you want to check the effectiveness of a drug, specifically a antidepressant. We do not know what positive and negative effects this medicine has on health, but what is expected is that it will help to raise the mood in people with depression.

100 volunteers with depression are submitted to the study. As we want to know the real effectiveness of this drug, we separate these 100 participants into two groups, with 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 actually a placebo, that is, a substance without any type of effect on the health.

The reason why half of the participants are not given the antidepressant is basically to prevent the placebo effect from biasing the research results. The placebo effect occurs when a person, Unconsciously, you notice improvement because you have been told that the treatment you have received has therapeutic power. It may not heal at all, but since the person wants it to do so, he begins to notice improvements that are not real.

By creating a control group and an experimental group it is easier to know to what extent the real drug effects changes, and which changes in particular. Any improvement seen in the experimental group that is not seen in the control group will be attributed to the therapeutic power of the experimental drug. In blinded studies, no participant knows whether they have received the drug or the placebo, so there is less possibility of fictitious improvements, this being the main advantage of this type of study.

The problem with this type of study is that the researchers do know which participants receive the real treatment and which receive the placebo treatment. This may seem obvious and necessary, but it is also a source of bias. It may be the case that the researchers believe they see significant improvements in the experimental group that, in reality, do not exist (observer effect).

In addition, it may be that at the time of randomizing the participants, and having some go to the control group and others to the experimental group, the participants themselves researchers consciously choose to enroll certain patients because they believe that they have a good chance of improving by receiving the treatment experimental. This is not entirely ethical, since this would "inflate" the results.

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Further double-blind studies

Fortunately, to overcome the limitation of blind studies there are double-blind studies. To avoid the bias attributed to the placebo effect and, also, the bias attributed to the observer effect, Both participants and researchers do not know who is in the control group and who is in the control group. experimental. Because researchers do not know which participants receive the experimental treatment, they cannot attribute improvements to it until they have statistically analyzed the data.

The vast majority of researchers are professionals, of this there should be no doubt. However, there is always the possibility that the investigator unknowingly alerts the participant to the treatment she is receiving, causing him to discover which group he belongs to. You can even favoritism by giving the treatment to patients who you think will have a better response, as we have already discussed.

Because neither experimenters nor participants know who is receiving the treatment, the highest possible level of scientific rigor is achieved. The only ones who know who is part of each group are third parties, who will have designed a system of coding that will make each participant receive a treatment or not and without the experimenters knowing what they are giving. The researchers will know to whom they have given the treatment when, when studying the data, the codes of each participant are revealed to them.

Going back to the case of the pharmaceutical study, in this case we would have a pill that would be the real drug and another pill that would be the placebo, identical in appearance. 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 they should give him the pill found in a box with the number 001, and so on with the 100 subjects in the experiment, assuming that 50 will receive the treatment and 50 a placebo.

Once each participant has received the pills, the time stipulated in the experiment is allowed to elapse. Once the experiment has been completed and the data of each patient has been collected, who will have reported the changes they have noticed, their physiological state and other measurements, These data will be statistically analyzed.. It is at this time that the people who designed the coding system will inform the experimenters who has received the treatment and who has not. In this way, empirical evidence can be obtained as to whether the treatment works or not.

Bibliographic references:

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