Explain the difference between a single-blind and a double-blind experiment.

Before understanding about single and double-blind techniques, it is important that you understand the amazing power of the placebo effect. This is an interesting film about placebos and their effect.

Single Blind: A single-blind design is when the participant doesn’t know if they are in the “treatment group” or the “control (e.g. placebo) group”.

The treatment group in an experiment is the group that experiences the factor that the researchers hypothesize will have an effect. The control does not receive this treatment, but something in its place. In many studies the control group will receive a placebo.

For example, let’s say a new drug is designed to cure cancer (we wish!). The researchers want to see if the drug actually works. Because of the power of the placebo effect the researchers want to give half the participants the real drug and the other half a placebo pill. A single blind design would mean that the participants wouldn’t know which group they’re in. It should be easy to see why this is important in such studies that test the effects of a particular treatment; if participants know they’re not getting the actual treatment then the chances it’ll work are reduced.

Double Blind: In a double blind design neither the participant nor the person gathering the dependent variable data knows which group the participant is in. Of course at least one person knows, but this is not the person gathering the data. To use the cancer pill example above, they could do something like keep a secret file of who is receiving which treatment and this is not revealed to the Doctors who are monitoring the effects the pill is having on the cancer.

The double-blind technique is valuable to reduce researcher bias. It is only natural that a researcher would want to prove their own hypothesis right. When data is highly subjective there is the potential for researcher bias to affect results. Not knowing which treatment the participant is receiving is one way of reducing the chances researcher bias will influence the experiment’s results.

In animal experiments obviously the animals don’t have the cognitive capacity to figure out which condition they’re in, or that they’re even in an experiment. But the researchers will often not know. There’s no need to state that it’s a double-blind because it’s redundant and a single-blind is inaccurate. In this cause it can simply be called a “blind study” or “blind design”. 

A double-blind study is one in which neither the participants nor the experimenters know who is receiving a particular treatment. This procedure is utilized to prevent bias in research results. Double-blind studies are particularly useful for preventing bias due to demand characteristics or the placebo effect.

For example, let's imagine that researchers are investigating the effects of a new drug. In a double-blind study, the researchers who interact with the participants would not know who was receiving the actual drug and who was receiving a placebo.

A Closer Look at Double-Blind Studies

Let’s take a closer look at what we mean by a double-blind study and how this type of procedure works. As mentioned previously, double-blind indicates that the participants and the experimenters are unaware of who is receiving the real treatment. What exactly do we mean by ‘treatment'? In a psychology experiment, the treatment is the level of the independent variable that the experimenters are manipulating.

This can be contrasted with a single-blind study in which the experimenters are aware of which participants are receiving the treatment while the participants remain unaware.

In such studies, researchers may use what is known as a placebo. A placebo is an inert substance, such as a sugar pill, that has no effect on the individual taking it. The placebo pill is given to participants who are randomly assigned to the control group. A control group is a subset of participants who are not exposed to any levels of the independent variable. This group serves as a baseline to determine if exposure to the independent variable had any significant effects.

Those randomly assigned to the experimental group are given the treatment in question. Data collected from both groups are then compared to determine if the treatment had some impact on the dependent variable.

All participants in the study will take a pill, but only some of them will receive the real drug under investigation. The rest of the subjects will receive an inactive placebo. With a double-blind study, the participants and the experimenters have no idea who is receiving the real drug and who is receiving the sugar pill.

Double-blind experiments are simply not possible in some scenarios. For example, in an experiment looking at which type of psychotherapy is the most effective, it would be impossible to keep participants in the dark about whether or not they actually received therapy.

Reasons to Use a Double-Blind Study

So why would researchers opt for such a procedure? There are a couple of important reasons.

• First, since the participants do not know which group they are in, their beliefs about the treatment are less likely to influence the outcome.
• Second, since researchers are unaware of which subjects are receiving the real treatment, they are less likely to accidentally reveal subtle clues that might influence the outcome of the research.

The double-blind procedure helps minimize the possible effects of experimenter bias. Such biases often involve the researchers unknowingly influencing the results during the administration or data collection stages of the experiment. Researchers sometimes have subjective feelings and biases that might have an influence on how the subjects respond or how the data is collected.

In one research article, randomized double-blind placebo studies were identified as the "gold standard" when it comes to intervention-based studies. One of the reasons for this is the fact that random assignment reduces the influence of confounding variables.

Example

Imagine that researchers want to determine if consuming energy bars before a demanding athletic event leads to an improvement in performance. The researchers might begin by forming a pool of participants that are fairly equivalent regarding athletic ability. Some participants are randomly assigned to a control group while others are randomly assigned to the experimental group.

Participants are then be asked to eat an energy bar. All of the bars are packaged the same, but some are sports bars while others are simply bar-shaped brownies. The real energy bars contain high levels of protein and vitamins, while the placebo bars do not.

Because this is a double-blind study, neither the participants nor the experimenters know who is consuming the real energy bars and who is consuming the placebo bars.

The participants then complete a predetermined athletic task, and researchers collect data performance. Once all the data has been obtained, researchers can then compare the results of each group and determine if the independent variable had any impact on the dependent variable.

A Word From Verywell

A double-blind study can be a useful research tool in psychology and other scientific areas. By keeping both the experimenters and the participants blind, bias is less likely to influence the results of the experiment. 

A double-blind experiment can be set up when the lead experimenter sets up the study but then has a colleague (such as a graduate student) collect the data from participants. The type of study that researchers decide to use, however, may depend upon a variety of factors, including characteristics of the situation, the participants, and the nature of the hypothesis under examination.

What is the difference between a single blinded and double blinded experiment?

What is a single blind in an experiment?

What is a double blind experiment and why are double blind experiments used?

What is a double blind experiment simple?