A controlled variable is not a Control Variable (CV).

Wait, What??! Now that’s just annoying! Why are they so similar but not the same thing??!

Yes, you can see how people get confused between the names of these variables, students and teachers alike, this is another good reason to think of the main variables (the ones in the table) as IV, DV, and CV. If you remember, the IV is the one thing we change to see what effect it has on the DV; how the DV changes. So, in order to see a change, you have to be able to make comparisons to what would normally happen, so you might have to do part of your experiment under completely normal conditions, so you can see what the changes in the IV do to the DV. 

Let’s take a different example to the fish experiment that is used on the Variables Overview page, let’s think about a standard experiment we often do in the lab:

“Type of liquid on plant growth“.

Quick quiz: Name the IV and DV - go!

We often perform this experiment and students choose liquids like Redbull, vinegar, lemon juice, coffee, their brother’s tears, etc. Now, if you have 9 plants and you give 3 plants vinegar every day, 3 plants lemon juice every day, and 3 plants coffee every day, you probably have a good idea what might happen to them. However, how can you be sure that the dead plants are because of the liquids? Maybe something else happened in the lab during the time you were growing them in their pots. A terrible gas leak, or a fungal infection from your classmates’ plants killed them……

To make sure you know it was the types of liquids that inhibited plant growth/killed them, you would have to have 3 more plants  growing next to them that you gave normal water to every day. If they were OK, then you can be more confident that it was the different liquids you used, rather than anything else.

Can you think of any other experiments you have done or might have to do that would need a variable to be controlled? 

For example:

So as you can see in the examples, some experiments are difficult to control with your CVs, 

AND you need to do a control test first.

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