He wrote a key psychology textbook. He trained a number of American psychologists in the late 19th Century. All of the above. None of the above. Whereas all experiments are ecologically valid, that term applies accurately to only some correlational research.
All variables are inherently correlational, and experimental manipulation is only an illusion.
Ethical concerns prevent psychologists from studying some phenomena experimentally. All of the above. Cues from the research environment that suggest that a particular type of behavior is expected. Announcements by the researcher that a particular pattern of behavior will probably be found. None of the above.