The Hawthorne Effect is a phenomenon in industrial psychology first
observed in the 1920s. It refers to improvements in productivity or quality
resulting from the mere fact that workers were being studied or observed.
Pygmalion Effect (or Rosenthal effect) refers to situations in which students performed
better that other students simply because they were expected to do so.
Placebo Effect is the phenomenon that a patient‘s symptoms can be
alleviated by an otherwise ineffective treatment, apparently because the
individual expects or believes that it will work
The John Henry Effect has also been identified: an experiment may spur competition between
groups, precisely because they are conscious of being part of an experiment.
The term ―halo effect‖ describe what happens when a scientific observation is influenced by
the observer‘s perceptions of the individual procedure, or service that is under
observation. The observer‘s prejudices, recollections of previous observations,
and knowledge about prior observations or finding can all affect objectivity
and must be guarded against.