How do you call a study in which subjects were deceived about the real purpose? Is there any “official” term to describe a study in which subjects were deceived about the real purpose of the research?

I am talking about studies that purposefully hide the real research questions from the subjects so as to prevent demand effects from influencing the results.

To make it more explicit: In my case, I tell people to watch a series of video clips from an online portal to describe the contents. What people don't know is that some of the videos are (purposefully) significantly distorted. I record their reactions to it (e.g. physiogically) — but people still think they're just describing videos.
The relevant section 8.03 in the APA Ethical Principles of Psychologists and Code of Conduct does not employ a proper term. In the literature, »deception/deceptive study/experiment/method(s)« are sometimes used, however not in the sense of a technical term – most often the matter is paraphrased as in »studies that use deception«.

The Milgram experiment(s) prominently employed deception, and the latter is most often discussed in the context of social psychology. On the other hand, there are much less clear cases. Robin Kramer in his comment is right that often it is not clear for the subject which variables are actually measured by some technique in a straightforward sense – think of a questionnaire that is part of a job application procedure, or e.g. indirect techniques for measuring attitudes.

Since deception as a clear-cut methodical device has been prominently used in social psychology, let's take a look at a popular text book:


  In this kind of experiment, it’s essential that the participant experience contrived events as if they were real; this is called a deception experiment. Deception in social psychological research involves misleading participants about the true purpose of a study or the events that transpire. (Aronson/Wilson/Akert/Sommers (2016): Social Psychology (9th ed.), p. 46)


Finally, Aronson et al. (2016) give the following references:


Christensen, L. (1988). Deception in psychological research: When is its use justified? Personality and Social Psychology Bulletin, 14, 664–675.
Epley, E., &amp; Hu , C. (1998). Suspicion, affective response, and education benefit as a result of deception in psychology research. Personality and Social Psychology Bulletin, 24, 759–768.
Finney, P. D. (1987). When consent information refers to risk and deception: Implications for social research. Journal of Social Behavior and Personality, 2, 37–48.
Gerdes, E. P. (1979). College students’ reactions to social psychological experiments involving deception. Journal of Social Psychology, 107, 99–110.
Sharpe, D., Adair, J. G., &amp; Roese, N. J. (1992).
Twenty years of deception research: A decline in subjects’ trust? Personality and Social Psychology Bulletin, 18, 585–590.