Developing an experiment to test a hypothesis
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To complete this task you will need to understand the following terms.
Independent Variable: This is the factor which the experimenter intentionally changes between groups in the experiment. It corresponds to the “if” part of the hypothesis. For example, if the hypothesis states: If a person is exposed to more minutes of sunlight then the person’s skin will be more severally burned. The independent variable would be the minutes of sunlight the person is exposed to.
Dependent Variable: This is the factor which the experimenter will measure. It corresponds to the “then” part of the hypothesis. In the above example the severity of the sun burn is the dependent variable.
Controlled Variables: These are factors which are held the same in all the groups of subjects. For example for the above hypothesis one controlled variable would be the complexation of the people in the experiment. You would ideally want all the subjects to have the same initial skin color. Another variable would be the time of day that the people were exposed to sunlight. Another variable would be the amounts of clouds in the sky during the time the people were exposed to sunlight. There can be several controlled variables in any experiment.
Control Group: that group of subjects in which the independent variable is either set to zero or is set at the normal value of the variable. For example in the above experiment the control group could spend no time in the sun. Alternatively, in another experiment testing the effect of different levels of water consumption over a period of several days you would not have the control group get zero water since this would adversely affect their health. You would have them consume a “normal” volume of water.
Experimental Group: that group or groups of subjects in which the independent variable is set at a value different from that of the control group. There can be several experimental groups in a given experiment. For example in the above experiment the experimental groups might be exposed to sunlight for the following times: 15 minutes, 30 minutes, 45 minutes, 60 minutes. In this case there are four experimental groups. Both the control group and the experimental group(s) have the same values for the controlled variables. For the above example both the control group and all four experimental groups would be composed of individuals with red hair and fair skin, they would all be exposed to the sun between 1 and 2 o’clock in the afternoon, and the experiment would only be performed on a day with no clouds.