A double-blind study is an experimental method used to guarantee impartiality and avoid errors derived from bias from both the participants and the researchers themselves. Although “classic” studies with a control group and an experimental group work, they are not as safe as the double-blind ones, in which not even the researchers themselves know who they are giving the experimental treatment to. Double blind study definition
Below we will see in depth how these types of studies work, in addition to a review of the placebo effect concept, 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 an investigation from being influenced by the placebo effect , originating from the research participants, and the observer effect, caused by the researchers themselves. These types of 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 both the participants and the researchers do not initially know who the subjects are in the experimental group and which subjects are in the control group .
Thus, the researchers do not know which participants are receiving the treatment or condition they want to know what effects it has, and they do not know which participants receive a condition with no effect (placebo). Double blind study definition
It is an important scientific invention and aims to avoid conscious or unconscious interference when experiments with human beings are carried out. Interferences that can happen unconsciously and affect the entire study. It is the type of study that best investigates the cause-effect relationship, as two groups with similar characteristics are used and the only difference is the administration or not of the medication, therapy or procedure under study.
It is an important study, as it is possible to discover whether a certain drug, therapy or procedure has a real therapeutic effect or not. When there is a suggestion for treatment (when we are told that we are going to receive some treatment), our body offers a biochemical response to the treatment, the so-called placebo effect. Hence the importance of the double-blind study.
In this type of experiment, there are two distinct groups: in one group, the drug/therapy/procedure you want to test is administered. In the other group, there is the administration of a substance that has no therapeutic efficacy, the so-called placebo . A placebo is any inert medication, therapy or procedure that has psychological effects on the patient, because he thinks he is being treated.
In the double-blind study, both the examinee, also called the object of study, both the examiner (or researcher) do not know which group each individual belongs to. The rationale for this technique is that when the patient knows they are receiving a new treatment, there can be a beneficial psychological effect on the patient, making them feel better even though there is no effective clinical improvement. And on the contrary, if the patient knows that he is receiving conventional treatment or no treatment at all, an unwanted psychological effect may occur. The patient may feel worse, even if there is no worsening in the condition. But this impact will depend on the type of illness and the nature of the treatment. Double blind study definition
The advantages of double-blind studies are:
- The risks of subtle and unrecognized differences in the quality and style of treatment, patient response, or investigator assessment decrease
- Are important when the result of the experiment requires subjective evaluations
The disadvantages of double-blind studies are:
- They are unfeasible when the intervention cannot be hidden from the patient and/or physician (different types of treatment, side effects)
Blind studies
In scientific research, blind studies are very important tools that allow avoiding 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 fully understand how blind studies work, we are going to put a hypothetical case of a pharmaceutical investigation, in which we want to verify the effectiveness of a drug, specifically an antidepressant. We do not know what positive and negative effects this medicine has on health, but what is expected is that it helps to raise the mood in people with depression.
100 volunteers with depression come to the study. As we want to know the real effectiveness of this drug, we separated these 100 participants into two groups, with 50 people each. One will be the experimental group, who 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 effect on health. Double blind study definition
The reason 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 notices improvement because they have been told that the treatment they have received has therapeutic power . It may not cure at all, but as the person wants it to do so, they begin 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 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 they have received the drug or the placebo, thus there is less chance of sham improvements, this being the main advantage of this type of study.
The problem with these types of studies 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 making some go to the control group and others to the experimental group, the researchers themselves consciously decide to incorporate certain patients because they believe that they have a great chance of improving receiving the experimental treatment. This is not entirely ethical, since if so, the results would be “bloated”. Double blind study definition
The advances of Organic Chemistry in the 19th century, together with the research methods developed, provided Medicine with the necessary tools for the birth of objective clinical research . In the 1930s, the main characteristics of the clinical research model were formalized, whose main components, according to Wojciechowski (1984) are:
- A clearly defined study population ,
- The random assignment to the various treatments of the independent variables
- Standardized methods for measuring results
- The incorporation of statistics
- The comparison with placebo or control groups without treatment.
The principle of using control groups has been known for more than 2,000 years . Instead, the principle of randomization was formulated only towards the end of the 19th century (Krauth, 2000).
The introduction of double-blind research in the Medical Sciences has represented a major milestone and gave the impetus to leave behind a long period based on superstitions and beliefs. The verification of the efficacy of drugs through controlled studies has meant the entry of medical therapy into the field of science. Likewise, the research developed in the field of psychotherapy and its results has been developed since 1952, after Eysenck published The effects of psychotherapy: An evaluation (Carr, 2009; Freeman & Power, 2007; Rubin, 2008; Santibáñez Fernández, Román Mella & Vinet, 2009)and it has been methodologically refined over the last decades with the introduction of experimental designs and statistics . (Cazabat, 2014) Double blind study definition
The blind experiment
The blind experiment is the basic requirement for any test of subjects and opinions. Failure to comply with this principle can lead to experimental defects .
The idea is that the groups studied , including the control group, should not know which group they are in . In medicine, when researchers are testing a new drug, they make sure the placebo looks the same and tastes the same as the real drug.
There is strong evidence for the Placebo Effect , where if people believe they are receiving a drug, they show some signs of improved health. A blinded experiment reduces the risk of bias from this effect, providing an honest baseline for the investigation and allowing a realistic statistical comparison .
Ideally, the subjects would not know that a placebo is being used, but this is considered unethical.
What is a double blind experiment
The Double Blind experiment takes this precaution against bias one step further by ensuring that the researcher does not know which group a patient falls into .
While the vast majority of researchers are professionals, there is always the possibility that the researcher will unconsciously alert a patient to the pill they are receiving. You can even play favorites by giving the pill to patients you think have the best chance of recovery, thereby skewing the results . Double blind study definition
While no one likes to think that scientists are dishonest, there is usually pressure from million dollar pharmaceutical companies, the struggle for research grants and pressure for positive results arises.
That is why there is always the possibility that a scientist will manipulate the results to try to show the research in a more favorable light . Demonstrating that the researcher conducted a double-blind experiment reduces the possibility of criticism.
Other applications of double blind experiments
Although the Double Blind Experiments are better known in medicine, they are also used in other fields. Surveys, questionnaires, and market studies use this technique to maintain their credibility .
If you want to compare two brands of powdered soap, the samples must be in the same container. A consumer could have a built-in awareness of a brand’s identity and a preference, so there would be favoritism and bias.
An example of the weakness of single-blind techniques is in police reconnaissance rounds, where a witness picks a suspect from a group. Many jurists argue that these wheels should be spontaneous and should not be supervised.
If the police are obsessed with bringing a certain subject to justice, they can consciously or unconsciously alert the witness. People are very good at understanding body language and unconscious signals. Therefore, the probability of observer bias should be minimized.
