In which type of research would an investigator manipulate at least one factor and observe its effect on some behavior or mental process?

A) the survey
B) the case study
C) experimentation
D) naturalistic observation

Only in experimentation can an investigator manipulate a factor and observe its effect on behavior or mental processes. In a survey, the investigator simply asks questions and does not manipulate anything. In a case study, the investigator observes an individual or group without manipulating any factors. In naturalistic observation, the investigator simply observes behavior without manipulating anything.