The manufacturer of Sleepeze has asked you to test the effectiveness of the drug. You decide to test the
effectiveness using the drug and a placebo. You select a select a group of 500 subjects and randomly assign them to either the treatment group or the placebo group.
Is this an observational study or a designed experiment?
What is the explanatory variable?
What is the response variable?
If this is an experiment, diagram the experiment.
You decide to “double blind” the study. What does that mean?
An independent variable (explanatory?) is the potential stimulus or cause, usually directly manipulated by the experimenter, so it could also be called a manipulative variable.
A dependent variable is the response or measure of results.
Extraneous variables — other than the independent variable — potentially can affect the dependent variable, so they must be controlled. If possible, you try to keep them constant between the experimental and control group.
The experimental group receives the independent variable.
The control group is similar to experimental, except it does not receive the independent variable. Extraneous variables are balanced between experimental and control groups.
Types of experiments
1. Single blind gives the control group a placebo — a substance that is inert, it has no physical effect. Subjects don't know if they are in experimental or control group to reduce placebo effect, a change in behavior solely due to believing that you are getting the independent variable.
2. Double blind keeps both subjects and experimenter ignorant of group setup. Distribution of the independent variable and placebo are controlled by third party. This controls for experimenter bias and self-fulfilling prophecy, which means that experimenters with particular expectations are likely to consciously or unconsciously to bias the experiment and influence it to conform to their expectations.
As an example, suppose you want to find out if fluorides reduce dental cavities. You would find two groups, trying to control the extraneous variables. Extraneous variables are found by surveying previous research in the area. In this case, you would match the groups in terms of previous history of cavities, diet and dental hygiene habits including how and how often they brush their teeth.
The experimental group would get toothpaste with the independent variable, the fluoride, while the control group would not have the fluoride in their toothpaste. The toothpaste without the fluoride would be the placebo.
The dependent variable would be the number of cavities after participating in the experiment for a time. The dependent variable indicates the results, but it is not the results. At the end of the experiment, both groups could have no change in cavities or one of the groups could have a greater reduction in cavities. (Of course, if the fluoride increased cavities, you wouldn't want to use it.) All of these varied results would be indicated in terms of the dependent variable.
If only the subjects do not know who is getting the fluoride, it is a single blind experiment. If both the subjects and experimenter do not know, it is a double blind.
This is a designed experiment.
The explanatory variable in this experiment is the use of the drug Sleepeze.
The response variable is the effectiveness of the drug in helping subjects sleep.
In order to "double blind" the study, it means that both the subjects and the researchers involved in the experiment are unaware of which group (treatment or placebo) each subject belongs to. This is done to minimize bias and placebo effects in the results. To achieve this, the drug and the placebo are typically packaged and labeled in a way that does not reveal their identity, and the assignment of subjects to the treatment and placebo groups is done randomly.