Single-Blind and Double-Blind Experiments

When we learned about sampling biases, we talked about the importance of single-blind and double-blind experiments to protect from these biases.

Single-Blind Experiments

A single-blind experiment is when the participants do not know which IV group they are a part of. The goal of single-blind experiments is to protect from biases that may impact a participant's performance.

Let's talk through an example.

Harold wants to test a new drug, Hondoclaride, on people's moods. Hondoclaride is supposed to make people angry. He gives half of the participants a placebo, and he gives the other half of the participants a dose of Hondoclaride. However, he doesn't tell the participant which injection they got. Say Jenny got a dose of Hondoclaride, and Harold tells her that. Jenny starts to feel angry.

How do we know that Jenny feels angry because of the Hondoclaride, or because that's what she thinks she's supposed to feel?

That's where a single-blind experiment comes in! Harold can give Jenny a dose of Hondoclaride but not tell her that he did. That way Jenny won't know whether she got the placebo or Hondoclaride. Now, if Jenny feels angry, we can speculate that it's due to the Hondoclaride.

Single-blind experiments are designed to protect against any biases that may influence the research outcome. In single-blind experiments, the participant doesn't know which level of IV they're assigned to, but the researcher does.

Double-Blind Experiments

Double-blind experiments are similar to single-blind experiments, but have one key difference. In double-blind experiments, neither the participant nor the researcher knows what group/level of IV the participant is assigned to.

If neither the researcher nor the participant knows the level of IV the participant is assigned to, we can still determine the research effects. A research team is made up a bunch of people, so a coordinator on the team will be able to separate which participants are in which group. It's cool!

So, now let's talk go back to the previous example with Hondoclaride.

We could make that experiment a double-blind experiment is neither Harold, the researcher, nor Jenny, the participant knew whether Jenny got the placebo or the dose of Hondoclaride.

Similar to single-blind experiments, we use double-blind experiments when we want to reduce bias in our research.

Examples

Now, it's your turn! Answer the next couple of example problems by yourself.

Explanation:

Because neither Maria nor the participant knows the level of IV the participant is assigned to, this is a double-blind experiment. A double-blind experiment is most effective in this research study in order to eliminate both participant and researcher bias.

Try the next example.

Explanation:

In this experiment, the researcher knows which cup has Coke and which cup has Pepsi, so there's no reason to protect against researcher bias, since that's very limited in this study. It is important to protect against participant bias, so Gary and Sasha should not tell the participant which cup has which soda!

(Video) Double Blind Study

by Practical Psychology

In this cute animated video by Practical Psychology, you will learn about the methodology of the double blind experimental design.

Single-Blind and Double-Blind Experiments

A blind procedure is one in which the participants and/or researchers are unaware of certain key aspects of the study, such as treatment assignments or outcome assessments. We often see blind procedures in randomized clinical trials and other clinical studies.

In a single-blind experiment, the participants are not aware of which treatment they are receiving, but the researchers are aware. This type reduces the potential for bias in participants but still leaves room for bias in the researchers.

In a double-blind experiment, neither the participants nor the researchers know who is receiving the experimental treatment and who is in the control group. This type helps to reduce bias in both the participants and the researchers, leading to more reliable results.

Triple-blinding is funky. This type involves not only keeping the participants and researchers blind to the treatment assignments, but also keeping other individuals involved in the study, such as data analysts, blind to the treatment groups. Now we can even further reduce the risk of bias.

Other key terms to keep in mind:

• The control group is a group of participants who do not receive the experimental treatment. They are used as a comparison against the experimental group to assess the effectiveness of treatment.
• The experimental group (aka the treatment group) is the group of participants who receive the experimental treatment or intervention being studied.
• Placebo control involves giving participants in the control group a treatment that appears identical to that in the experimental group, but contains no active ingredient. The placebo control helps to control for the placebo effect.
• Observer bias happens when the researchers' expectations or beliefs influence their interpretation of the results or their observations of the participants' behaviors.