Step 2 Defining Variables and Writing Hypotheses

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There are some great examples of how, questions, hypotheses and variables are related here.

1. Define Your Variables


Variables are anything that might change or be changed in an experiment. Some variables you will change yourself. Other variables are the ones you are interested in measuring. There are three main types, Independent or Manipulated variables and Dependent or Responding Variables, and Control variables.

Independent or Manipulated Variables


This variable is something that you change when you do your experiment. If your question is very clear, you can take the independent or manipulated variable right out of the question.


Example
independent_variable.gif
This is the thing I will change during the experiment. It is the only thing that should change.

Dependent or Responding Variables

Often times you are looking to see if the Dependent or Responding variable will change when you do your experiment. In other words, the dependent variable depends on the independent variable. Another way to say this is that the Responding Variable responds to what you have manipulated (manipulated variable). This is often the main thing you will measure. Again if you have written a really clear question you will find your dependent or responding variable right there in the sentence!

Example
dependent_variable.gif
This is the thing I will measure during the experiment.


Variables that need to be controlled


The Controlled Variables refers to the fact that only one thing should change in an experiment and that you should be in full control over that one thing. You will have a hard time drawing solid conclusions from an experiment without a good control.
Example
In my example I will use basil plants that are grown exactly the same in every way (water, time in light and dark, soil, temperature, location...) except for the wavelength of light.




2. Formulate a Hypothesis


Your hypothesis should predict the outcome of the experiment. What do you think will happen. The hypothesis should include references to both the Independent and Dependent Variables. Keep this simple and the next step will be a snap!
Example It is hypothesized that the wavelengths from fluorescent lights will produce the smallest gain in basil plant biomass.



3. Graph Your Hypothesis


At this point you know what you will be measuring (variables) and what you think will happen (hypothesis). From this you should be able to draw a graph of what your results would look like if your hypothesis were true. If you can do this your experiment is half over. All that is left is to do it! I used Paint to make the graph but you could use any drawing program (since you have no data). When you save the image of the graph you must save it as a .gif, .png, or .jpg as these are the only file formats that will work. Then you can just upload the image. Here is a good tutorial.

Example
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4. Variables and Hypothesis Rubric



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