Design Experiments to Test Your Hypothesis Design an experiment to test each hypothesis. This list is called an experimental procedure. A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed.
Dependable controls are sometimes very hard to develop.
They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. Experiments are often done many times to guarantee that what you observe is reproducible, or to obtain an average result. Reproducibility is a crucial requirement. Without it you cannot trust your results.