In our last meeting, we discussed the scientific method. I covered a vital part of the scientific method, design and run an experiment, but I’d like to expand a little on that today.

In an experiment, I said we’re always going to have two groups that we test. The first group, the control group, tells us what would happen without our interaction. The second group, the variable group, tells us what happens when we perform our experiment. If our experiment was to test the amount of growth of plants by adding fertilizer, our setup would look something like this:


You can see that only 1 thing separates our control group from our variable group. Our variable, then, is the fertilizer. The variable you choose to change is called the independent variable. The variable that changes based on what you do in the experiment is called the dependent variable.

Note: When designing an experiment be careful to not have more than one independent variable. In the event of more than one, you cannot be sure as to which variable actually resulted in the change you’re measuring. For example, in our experiment if we changed both the amount of water we gave the plants and whether or not we used fertilizer, we couldn’t be sure as to whether a change in plant growth was because we used fertilizer or because some plants didn’t get the same amount of water as the others.

In our example experiment, our independent variable is the fertilizer (specifically, the amount we use). A way to remember this is that it’s the independent variable because it is independent of what’s going on in the experiment. Only the experimenter decides how much fertilizer to use. Our dependent variable is the plants’ growth (the amount of growth measured). A way to remember this is that it’s the dependent variable because it is dependent on the other variable. The amount of plant growth is only affected by how much fertilizer we used.

In an effort to not overload you today, I’ll call it quits. Next time, we’ll have a talk about some famous experiments and how they were improved upon by other scientists. In the meantime, feel free to leave me messages, comments, or questions. You can do that here, on my about page, or on my new Twitter account: @amoebamike


One Response

  1. I thought you’d be interested in They Might Be Giants, a singing group whose most recent album is “Science Is Real.” They were featured on Ira Flatow’s Science Friday (Nov. 27, 2009) and sang the album title that includes a lyrical explanation of the scientific process. Keep up the good work of making science understandable and important to your students and your blog readers.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s

%d bloggers like this: