Double-blind study: characteristics and advantages of this design.
Summary of the characteristics and functions of this type of research design, the double-blind.
A double-blind study is an experimental method used to guarantee impartiality and avoid errors arising from bias both of the participants and of the researchers themselves.
Although "classic" studies with a control group and an experimental group work, they are not as safe as double-blind studies, in which not even the researchers themselves know to whom they are giving the experimental treatment.
Next 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.
What is a double-blind study?
Double-blind studies are a type of scientific research used to prevent the results of research from being influenced by the placebo effect, originating in the research participants, and the observer effect, caused by the researchers themselves.The placebo effect, originating in the research participants, and the observer effect, caused by the researchers themselves. This type of study is very important in many fields of research, especially in the health and social sciences.
The main aspect of double-blind studies is that both the participants and the researchers do not initially know who the subjects are. do not initially know which subjects are part of the experimental group and which subjects are part of the control group..
Thus, the investigators do not know which participants are receiving the treatment or condition that they want to know what effects it has, nor do they know which participants are receiving a condition with no effect (placebo).
In scientific research, blinded studies are very important tools that make it possible to avoid biases related to participants' perception of the experimental treatment they receive. avoid biases related to the participants' perception of the experimental treatment they receive.. It is important to understand this type of study before going into details about double-blind studies, and for this reason we are going to talk at length about what blind studies are like.
In order to understand how blind studies work, let's use a hypothetical case of a pharmaceutical research, in which we want to test the effectiveness of a drug, specifically an antidepressant. We do not know what positive and negative effects this drug has on health, but what is expected is that it will help to elevate the mood of 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, i.e. a substance with no effect on health.
The reason why half of the participants are not given the antidepressant is basically to prevent the placebo effect from biasing the results of the research. The placebo effect occurs when a person, unconsciously notices improvement because they have been told that the treatment they have received has therapeutic power.. It may not cure at all, but because the person wishes it did, he or she 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 actual drug exerts changes, and what changes in particular. Any improvement seen in the experimental group that is not observed in the control group will be attributed to the therapeutic power of the experimental drug. In blind studies, no participant knows whether he/she has received the drug or the placebo, so there is less chance of fictitious improvements, which is 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 researchers believe they see significant improvements in the experimental group that, in reality, do not exist (observer effect).
In addition, it is possible that at the time of randomizing the participants, and having some go to the control group and others to the experimental group, the researchers themselves may consciously decide to include certain patients because they believe that they have a good chance of improving by receiving the experimental treatment. This is not entirely ethical, since this would "inflate" the results.
The most in-depth double-blind studies
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, both participants and researchers do not know who are in the control group and who are in the experimental group. Since 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 there is always the possibility that the researcher may unconsciously alert the participant to the treatment he or she is receiving, causing him or her to discover which group the participant is in.The researcher, however, may unconsciously alert the participant to the treatment he or she is receiving, causing him or her to discover which group he or she belongs to. He may even play favorites by giving the treatment to patients whom he believes will have a better response, as we have already mentioned.
Because neither experimenters nor participants know who is receiving the treatment, the highest level of scientific rigor is achieved. The only people who know who is in each group are third parties, who will have designed a coding system that will result in each participant receiving a treatment or not and without the experimenters knowing what they are giving. The researchers will know which people have been given the treatment when, at the time of studying the data, the codes of each participant are revealed to them.
Returning 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 should be given 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 pass. Once the experiment has been completed and the data collected from each patient, who will have reported the changes they have noticed, their physiological state and other measures, the data will be statistically analyzed.. It is at this point that the people who have designed the coding system will inform the experimenters who have received the treatment and who have not. This will provide empirical evidence as to whether or not the treatment works.
- Hróbjartsson, A; Emanuelsson, F; Skou Thomsen, AS; Hilden, J; Brorson, 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.; Hróbjartsson, 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
(Updated at Mar 28 / 2023)