dentifying Dependent and Independent Variables
In order to test a hypothesis and prediction, controlled experiments are used. Controlled experiments involve several necessary components. An independent variable is usually manipulated by a researcher but does not change as a result of the experiment. The changes in the dependent variable may be caused by the experiment (and depend upon the independent variable). Graphs that depict the experimental data list the independent variable on the x-axis while the y-axis shows the dependent variable.
A commonly used mnemonic (memory device) to aid in distinguishing the characteristics of the types of variables is DRY MIX.
D = dependent variable (depends on the other)
R = responding variable (one that changes)
Y = y-axis on a graph
M = manipulated variable (one that is changed by the researcher)
I = independent variable
X = x-axis on a graph
The following sentence is a template to write an if/then statement to be used as a prediction:
If the independent variable is changed [increased, decreased, etc.], then the dependent variable will change in this way [increase, decrease, etc.].
Example: If the amount of available light increases, then plant growth will increase.
Discussion Questions:
Use the tools and examples just discussed to answer the questions about the experiment scenario described next.
Jonah and Tessa noticed that some Leopard frogs by a local river had extra limbs. They decided to check various areas along the river to make more observations. They recorded their observations in their field notebooks. Jonah and Tessa performed a simple laboratory experiment with Leopard frog eggs and river water taken at various spots along the river. They noticed that adult frogs developing from eggs in water collected near an industrial park showed more deformities, but the deformities seemed to be different than those seen on frogs in the natural setting by the river.
Write a prediction that would be appropriate for the experiment scenario.
What would be the independent variable in the experiment?
What would be the dependent variable in the experiment?
What steps should Jonah and Tessa take to ensure that the experiment would be controlled?
Why would they perform these experiments in the laboratory and not in the river?
What conclusion should the researchers derive from their data?
What might be some alternative hypotheses for this situation?
What could be a next step for their investigation?
What other information may help them design future experiments?
