controlled experiment

A controlled experiment is an experiment that is only changing one factor.  The independent variable is only changing one thing to see how it effects the dependent variable.  We did an experiment in class to see how different conditions change the growth of corn. In the corn experiment there was the option to add bugs.  If you added the bugs you found that, they damaged the overall yield of the corn.  The other way you can change the experiment is by changing the variety of corn.  If you want a controlled experiment then you have to do one at a time(bugs or variety). This is just one example of a controlled experiment.  In drug testing we usually use animals to test how a drug effects you.  A placebo is a drug in example, for people who need something to give them the will power to live.  It is basically a sugar pill given to make them think it is healing them.  It isn't exactly to tick them as much as to see if medicine will even help.  Its like a thing to make the people think they are on medicine will the doctor can see what will happen with no medicine.