When using the scientific method to solve a problem or
question, one formulates an educated guess or hypothesis which is a possible answer to
the problem or question. In order to test your hypothesis, you perform an experiment. An
experiment is set up to test the effect of a variable on an outcome. This variable that
the experimenter manipulates is known as the independent variable. If some change occurs
as a result of the independent variable, this change is the dependent
variable.
If you set up an experiment, you need a standard
of comparison to see if any change occurs as a result of your independent variable.
Therefore, you divide your experiment into two groups. The experimental group and the
control group. The experimental group or the manipulated group, gets the variable you
are testing. However, the control group, does not get the variable. At the end of the
experiment, you compare the data from both groups to see if your hypothesis was correct
or not. For example, if I want to test the hypothesis that plants grow best if given a
new plant food, then, if I have 500 plants for instance, I would divide my plants into
two groups of 250 plants. The first 250 plants, or the experimental group would be
given the plant food. The presence of this plant food is the independent variable I am
manipulating. The other 250 plants are the control group. They will not receive any
plant food.
I will collect data for several days or weeks.
This data would be measurements of the height of my plants in both groups. All other
variables must be the same in both groups--amount of light, water, type of pots, soil,
etc. The only variable that is different would be the plant food given to the
experimental group. At the end of the study, I will analyze the data, and see if I will
accept or reject my hypothesis. A good experiment should be re-tested several times to
make sure the results are accurate!
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