An optometrist is interested in the effects of different brands of eye drops. She wants to know if different drops affect the accuracy of a standard vision test. Some researchers think that Brand A may have more adverse effects on an individual's ability to correctly report the letters in the vision test than Brand B or Brand C. There is also some speculation that the effect of the drops on vision differs dramatically for individuals who are far-sighted compared to those who are near-sighted.

The optometrist hires you to design an experiment that tests the effect of the eye drops on test performance. You tell her there are two possible approaches to take: a randomized comparative approach or a matched pairs design. Describe how you would use each design to test the effect of the eye drops on test performance on a random sample of patients. Remember, there is a concern about the effects for near vs. far-sighted patients. As much as possible, use diagrams instead of words to summarize your experimental design. (7 points)