Dependent and independent variable When designing an experiment, a scientist needs more than an experimental,

dependent and independent variable. The scientist also needs an experimental group and a control group. The experimental group contains subjects that receive the manipulation of the experimental variable. The control group contains subjects that are exactly the same as those in the experimental group, except that they do not receive the manipulation of the experimental variable.
Why is a control group necessary? Without one, the results of an experiment may be meaningless. The control group serves as a comparison with the experimental group. There are two different kinds of control groups: negative, and positive. Negative control groups do not receive the manipulation of the experimental variable. Instead they receive a treatment that contains no active ingredient, this fake medicine is called a placebo. Positive control groups do not receive the manipulation either, but they do receive a different kind of manipulation – one whose effects are known. For example, in a tumor study, a positive control group would have received a drug that is already known to shrink tumors.
The rancher has 25 goats that receive an injection of Vitamin A, 25 goats that receive an injection of saline and 25 goats that receive an injection of Melatonin.  The rancher has read published scientific articles that have shown that melatonin increases the growth of goat hair.
Match the group of goats to the proper groups within the experiment.
1. 25 goats receiving a Vitamin A injection
A. experimental group
B. control group
C. Negative control group
D. positive control group
E. Variable Group
2. 25 goats receiving a saline injection
A. experimental group
B. control group
C. Negative control group
D. positive control group
E. Variable Group
3. 25 goats receiving a Melatonin injection
A. experimental group
B. control group
C. Negative control group
D. positive control group
E. Variable Group