Note: If more than $13,000 of debt is canceled in one year, the gift giver has to file a gift tax return (although they almost certainly will not owe a tax). That should not affect you as the recipient. Example: Roxy borrowed $6,000 from her dad while she was unemployed. She wrote up a promissory note for the debt.
Control Group and Experimental Group. True experiments must have a control group, which is a group of research participants that resemble the experimental group but do not receive the experimental treatment. The control group provides a reliable baseline data to which you can compare the experimental results.
1 A controlled trial is a study in which participants are assigned to a study group. Study groups are also called study arms or treatment conditions.  In a randomized controlled trial, participants are assigned to treatment conditions at random (i.e., they have an equal probability of being assigned to any group).