I believe the answer is: The presence or absence of music
independent variable refers to the type of variables that are not influenced by other variables. This represent the things that can be controlled by the researchers in order to ignite a certain causal relationship with the dependent variables ( the things they want to measure)
A store plays background music on some days, randomly chosen, and none on other days. It compares sales on the two kinds of days. The dependent variable in this experiment is the presence or absence of music.
