Another type of pollution is noise pollution. There is a growing concern over the physiological and psychological effects of noise pollution on human health. The following experiment describes a study that was performed to study the effects of noise pollution on a human’s ability to learn. A total of 200 10-year-old children of similar intellectual abilities participated in a noise experiment in their classrooms. They were tested for their ability to recall the meaning of a symbol in a textbook one week after the start of the experiment. Students did not know the meaning of the symbol prior to the experiment. The 200 students were split into 10 groups of 20 students and were taught the meaning of the symbol during a 15-minute lesson. Five groups learned the meaning of the symbol without any noise pollution outside of their classrooms. The other five groups learned the meaning of the symbol with a noise source of 55 decibels outside their classrooms, maintained continuously for the 15-minute lesson. One week after the lesson, 80% of the students who were not exposed to the noise sources were able to successfully recall the meaning of the symbol and 25% of the students exposed to the noise sources were able to successfully recall the meaning of the symbol.

i. Identify the dependent variable in the experiment.
ii. Describe the control for the experiment.
iii. Based on the described experiment, state a valid hypothesis for the experiment.
iv. Describe how the addition of insulation inside the walls of the classroom would most likely affect the results of the study.