Dr. DeLoss is interested in whether training can improve vision in older adults. He first measured visual acuity (clarity of vision) in a sample of 100 people. He then had a group of 50 participants completed a 15 minute training task once a day for one month. The other 50 people did nothing different in their routine. At the end of the month he had both groups participate in another visual acuity test to measure any changes in vision. Identify the independent and dependent variables.