The Hawthorne effect is a phenomenon in group-based observational research. It is an effect on an outcome variable caused by the fact that the participants of the study know they are participating in the study.

The theory speculates that a process is improved by the psychological stimulus of those being singled out and made to feel important. In other words, if participants know they are a part of an experiment that can lead to improved efforts of the people involved, this creates a distortion of research results caused by the response of participants to the special attention they receive from researchers.

The effect was first noticed in the Hawthorne plant of Western Electric during the Hawthorne studies. Production increased not because of actual changes in working conditions introduced by the management, but because management demonstrated an interest in such improvements (often referred to as Self-fulfilling prophecy). Experiments included altering lighting levels on the shop floor. Productivity increased when the lighting level was increased and increased again when lighting levels were reduced.

Along with Frederick Taylor's work, this study gave rise to the field known as industrial psychology. Social group influences and interpersonal factors must also be factored in when performing efficiency research such as time and motion studies.

External links:

• The Hawthorne effect
• The Hawthorne effect: a note