Experiments to test a hypothesis should consist of at least two parts.
- A test where one variable is changed.
- A control where that variable is unchanged.
All other factors that may affect the experiment should be kept the same.
In our hypothesis of exposure to UV-B,
a test group may be exposed to high levels of UV-B,
while a control group suffers no such exposure.
All other factors, such as age, sex and diet, should be kept the same.