Randomized Trial:
(1)    Study is blinded either single or double.  Randomization of patients into group A or B.  Once patients are separated, you make a hypothesis about the study–a “null hypothesis.”  You say you will find no difference in the outcome, so you look to see if there is a difference and if so, can it be attributed to chance or due to intervention itself?  Decision as to whether due to chance or intervention is based on probability statistics.