A student makes the hypothesis that rubbing a balloon on a shirt and then putting it on the wall will cause it to stick due to static electricity. Once the experiment is conducted, what is the best way to prove that the results are reliable?

The questions have been asked in several important state and regional science exams in the United States. For example: TAKS-Texas Assessment of Knowledge and Skills, New York State Educational Department Regents exams, California Standards Test, etc.