Single and Double Blind Designs

How are single blind and double-blind techniques used in experiments?

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.

[youtube https://www.youtube.com/watch?v=yfRVCaA5o18&w=560&h=315]

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”.