Independent Variable

This is the variable you are testing, or manipulating.
In our experiment, the independent variable was the type of cleaner.
We hoped that by changing the cleaner, we would see a change in the cleaning result.



Dependent Variable

This is the variable you are measuring.
For example, when you test each type of cleaner, you will measure how much stain is left. The amount of stain remaining each time you do the experiment would be the dependent variable.

(A major flaw in our experiment was that we didn't measure anything with numbers. The actual mass of each stain should have been the same (see below), and it should have been recorded. Then the remaining mass should have been measured, after cleaning. This would have provided a precise measure of how effective each cleaner was.)


Controlled Variables

These are variables that could affect the outcome of the experiment, which you make the same each time.
For example, each time you test a cleaner, you would use the same amount. It's not a fair test if a large amount of one cleaner is used, but only a small amount of another .
Similarly, you would make sure that each stain sample has the same mass, so that if one cleaner does a better job, you'll know it wasn't because there was less stain.
Most important of all, each cleaner should have been tested on all the stains. That way we could have found out how well each one cleaned each stain. It isn't a fair test if one cleaner has to clean peanut butter, and another ketchup. In fact, water is particularly poor at cleaning peanut butter. We never discovered that.

You're supposed to control  these variables, by  making them the same for every test, so you know they're not affecting the result. We didn't do that.

Some of the variables you might want to control in this experment would be:

• The type of stain.
• The amount of cleaner used.
• The amount of stain.
• The type of cleaning cloth.
• The time spent wiping.
• The number of wipes.
• The force used to wipe.
• The surface on which the stain is applied.
• The time the stain was allowed to sit before cleaning.

None of these things were the same in the three experiments, which means that we really don't know which cleaner is the best. It probably isn't water!

• We didn't control any of the other variables. Many of them probably affected the result.
• We didn't measure anything quantitatively. A good experiment generates results which are numerical measurements.
• We didn't test each cleaner on all the stains.
• Parts of our conclusion were not supported by the results:
  
  • Water was never tested on the other stains.
    
  • We didn't measure costs (water isn't free).
    
  • We never tried vinegar with the water.
• We didn't repeat the experiment. Conclusions should always be verified by repeating the test.
• We didn't analyze our results for possible measurement errors. (Because, of course, we never measured anything!)