The experimental group is the group who receives the critical part of the experiment, the treatment.This is the group who will listen to music while studying.
Experiments are the best way to determine cause and effect relationships between these variables.
Psychologists rely on random assignment to assign subjects to different groups in an experiment.
How will you decide who is in the experimental group and who is in the control group?
What about allowing students to choose which group they're in? Maybe the students who choose to listen to music are already better students who excel at focused studying. Okay, so how about picking the experimental group based on a first-come basis?
The important piece is that subjects are equally likely to be in the experimental group.
Random assignment is the best way to assure that the only difference between the control group and the experimental group is whether or not they receive the treatment.
The independent variable is that first factor: the one whose influence we're trying to measure.
An independent variable doesn't change based on the other variables.
Random assignment is the only way to eliminate other variables that could influence your results. There are a lot of different methods; the only requirement is that every subject has an equal chance to be in the experimental group.
Drawing names out of a hat or creating a lottery are ways to make assignment to the experimental group random.