A scientist wishes to determine how effective a vaccine is in protecting rats against a contagious disease. Which experimental procedure should the scientist use to determine the vaccines effectiveness?

A simplified summary of the experimental method might also be helpful.

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.

I hope this helps a little more. Thanks for asking.

To determine the vaccine's effectiveness in protecting rats against a contagious disease, the scientist should follow a controlled experimental procedure called a "vaccine efficacy trial." Here's how the scientist can set it up:

1. Acquisition and randomization: Obtain a group of rats that are free from the disease and randomly divide them into two groups: the vaccinated group and the control group.

2. Vaccine administration: Administer the vaccine to the rats in the vaccinated group. It is essential to follow the recommended dosage and administration guidelines provided by the vaccine manufacturer.

3. Control group: The control group should consist of rats that receive a placebo or an alternative treatment that does not provide protection against the contagious disease.

4. Disease exposure: Introduce the contagious disease to each group by exposing them to a controlled source of the pathogen. This could involve housing the rats in close proximity to infected rats or directly introducing the pathogen into the experiment environment.

5. Observation period: Observe both groups over a specified period of time, monitoring the development and progression of the disease in each individual. This could involve daily health checks, tracking clinical symptoms, or even conducting regular laboratory tests.

6. Data collection and analysis: Keep detailed records of each rat's health status, noting the presence or absence of the disease and any related symptoms. After the appropriate observation period, collect and analyze the data to determine the vaccine's effectiveness.

7. Statistical analysis: Use appropriate statistical methods to compare the incidence and severity of the disease between the vaccinated group and the control group. This analysis will provide insight into the vaccine's ability to protect against the disease.

By following this experimental procedure, the scientist can assess the vaccine's effectiveness in protecting rats against the contagious disease, providing valuable information for further development and potential human applications.