how we can improve our memory.

Dolly, a final year student, is interested in how we can improve our memory. She hypothesizes that experiencing classical music leads to an enhancement in short-term memory. For her research project, Dolly surveys 100 UG students who have had music lessons when they were in primary school. She asks the students to report their years of musical experience and to rate their own memory ability. Using statistical analyses, Dolly discovers that there is a strong positive correlation (r = 0.80) between classical music experience and memory ability.
Explain to Dolly why her finding is not strong evidence for her hypothesis. Then, design a study through which her hypothesis can be more rigorously tested. Describe the procedure, and explain the rationale behind your design. Should not exceed 400 words.