Fire

Three professors (a physicist, a chemist, and a statistician) are at a meeting when a fire breaks out in a wastebasket. The physicist says, "I know what to do! We must cool down the materials until their temperature is lower than their ignition temperature and  then the fire will go out."

The chemist says, "No! No! I know what to do! We must cut off the supply of oxygen so that the fire will go out due to lack of one of the reactants."

As the physicist and the chemist debate what to do, the Statistician actually does something. He runs around the room lighting more fires. The physicist and the chemist scream "What are you doing?"

The statistician replies, "We're going to need a larger sample size."