Why is a control set-up being done in the conduct of an experiment. Give Example.
An independent variable 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.
A control set-up is done in the conduct of an experiment to serve as a baseline or reference point for comparison against the experimental group. It is important because it allows researchers to isolate and measure the specific effects of the experimental variables.
Here's an example to illustrate this concept:
Let's say a scientist wants to investigate the effect of a new fertilizer on the growth of plants. The scientist sets up an experiment with two groups:
1. Experimental Group: This group consists of plants that are treated with the new fertilizer.
2. Control Group: This group consists of plants that are not treated with the new fertilizer, but are otherwise subjected to the same conditions (same soil, lighting, temperature, watering, etc.).
By having a control group, the scientist can compare the growth of the plants in the experimental group to the growth of the plants in the control group. Any differences observed between the two groups can then be attributed to the effects of the new fertilizer, as the control group serves as a reference point that represents "normal" growth.
If the plants in the experimental group grow significantly better than those in the control group, it suggests that the new fertilizer has a positive effect. Conversely, if there is no difference or if the plants in the control group grow better, it suggests that the new fertilizer does not have a significant impact on plant growth.
By having a control set-up in this experiment, the scientist can confidently draw conclusions about the effect of the new fertilizer, ruling out other factors that might affect plant growth.