In psychology, a single-blind study is a type of experiment or clinical trial in which the experimenters are aware of which subjects are receiving the treatment or independent variable, but the participants of the study are not.
A study in which both the experimenters and participants are unaware of who is receiving the independent variable and who is not is known as a double-blind study
Reasons to Conduct a Single-Blind Study
There are a number of reasons why researchers might opt to use a single-blind study. In many cases, it can be a way to prevent participants from changing their behavior.
Study participants will sometimes change how they behave simply because they are part of an experiment. Sometimes participants in a study will try to guess what a study is about or what they think the experimenters are hoping to find.
This can lead them to change their behavior, which can ultimately skew the results. A single-blind study can help prevent this or minimize the effects of such demand characteristics.
Demand characteristics are cues that might help participants guess the purpose of an experiment or study.
Example of a Single-Blind Study
For example, imagine that researchers are performing a study to determine if a certain type of medication causes people to feel more alert. If participants knew that the researchers were testing a hypothesis that the drug increased alertness, they might start acting more alert after ingesting the medication.
By using a single-blind procedure and not telling the participants what they are looking for, people are less likely to inadvertently bias the results by changing their behavior.
Research has shown that not using sufficient patient blinding in research can lead to significant bias in the results.
There are also times when unblinding may occur, which involves the participants becoming aware of their treatment condition or of the intentions of the experiment. Sometimes this happens when a participant is debriefed following an experiment, but it can also happen before a study ends, which can create problems with results.
Studies have found that nearly around 75% of participants in antidepressant studies are correctly able to guess their treatment condition. This can lead to bias, and in some cases, may exaggerate the effectiveness of the medications.
Moncrieff J, Wessely S, Hardy R. Meta-analysis of trials comparing antidepressants with active placebos. The British Journal of Psychiatry. 1998;172(3):227-231. doi:10.1192/bjp.172.3.227
Perlis RH, Ostacher M, Fava M, Nierenberg AA, Sachs GS, Rosenbaum JF. Assuring that double-blind is blind. AJP. 2010;167(3):250-252. doi:10.1176/appi.ajp.2009.09060820
U.S. Department of Health and Human Services. Single-blind study.