In the statement below, which is the independent variable and which is the dependent variable?
Renewable energy sources (solar and corn) are more environmentally friendly than fossil fuels. Therefore, within the next ten years renewable energy should replace fossil fuels.
The independent and dependent variables in this statement are not really as clear as they should be. That is, the dependent variable is clear, but the independent variable is not clear. The dependent variable is clearly the percentage of fuels of different sorts. It is the market share that is held by fossil fuels and renewables, respectively. The independent variable has to be the year, but this is not really what it should be.
In a research project, a researcher tries to look at how the dependent variable changes in response to the changes in the independent variable. The hypothesis is that a change in the independent variable will cause a change in the dependent variable.
In this case, the type of fuel being used is clearly what is supposed to change, but it really seems as if it should change in response to attitudes about the environment. That is what is suggested by the statement. I would think that the independent variable should be the degree to which people think that the environment is important. We could then hypothesize that more concern for the environment will lead to less use of fossil fuels. However, that is not what the statement says. The only variable that is mentioned other than the dependent variable is time. The statement is saying that the passage of time (independent variable) will cause a change in the kind of fuel that is used (dependent variable).