Experimental Research Design

Marsha, a dermatology student, is investigating whether consuming chocolate causes acne in fifteen-year-old girls. She conducts a controlled study with 20 fifteen-year-old girls, dividing them into two groups of 10. One group consumes chocolate daily for two weeks, while the other group consumes no chocolate during the same period. After recording her findings, Marsha concludes that there is no correlation between chocolate consumption and acne in this demographic. This research design is an example of _____.