Answer:
The scientist used the experimental statistical study.
Explanation:
Statistical study is the process of collecting, analyzing and presentation of data to achieve an accurate conclusion. The major types are: survey, and experimental.
Survey statistical study can easily be achieved by the use of questionnaires to sample the opinion of participants. While experimental statistical study involve the participants observing a process or some procedures before conclusions can be made.
In the given question, the scientist performed an experiment by asking participant to undergo a process before making his conclusion. Thus, he used an experimental statistical study.