To test the effect of music on productivity(number of products made per hour), a group of assembly line workers are given portable mp3 players to play whatever music they choose while working for one month. For another month, they work without music. The order of the two treatments for each worker is determined randomly.
a. Is this a survey, an observational study, or a controlled experiment? Explain your answer.
b. What is the explanatory variable in this study? What is the response variable?