Hawthorne effect
The Hawthorne effect describes a temporary change to behavior or performance in response to a change in the environmental conditions, with the response being typically an improvement.
The term was coined in 1955 by Henry A. Landsberger when analyzing older experiments from 1924-1932 at the Hawthorne Works (outside Chicago). Landsberger defined the Hawthorne effect as:
- a short-term improvement caused by observing worker performance.
Earlier researchers had concluded the short-term improvement was caused by teamwork when workers saw themselves as part of a study group or team.  Others have broadened the definition to mean that people's behavior and performance change following any new or increased attention.  Hence, the term Hawthorne effect no longer has a specific definition.
The Hawthorne studies have had a dramatic effect on management in organizations and how people react to different situations. Although illumination research of workplace lighting formed the basis of the Hawthorne effect, other changes such as maintaining clean work stations, clearing floors of obstacles, and even relocating workstations resulted in increased productivity for short periods of time. Thus the term is used to identify any type of short-lived increase in productivity. In short, people will be more productive when appreciated or when watched.
The term Hawthorne effect has been linked with numerous other terms, including: epistemic feedback, systemic bias, implicit social cognition, and continuous improvement.

# History
The term gets its name from a factory called the Hawthorne Works, where a series of experiments on factory workers were carried out between 1924 and 1932.
Many types of experiments were conducted, but the initial purpose was to study the effects of lighting on worker productivity. Researchers found that productivity almost always increased after a change in illumination but later returned to normal levels. This effect was observed for minute increases in illumination. Over time changes in illumination had no measurable effect probably due to regression brought on by the increased stress.
A second set of experiments began and were supervised by Harvard University professors, Fritz Roethlisberger and William J. Dickson. They experimented on other types of changes in the working environment, using a study group of five young women. Again, no matter the change in conditions, the women nearly always produced more. The researchers reported that they had accidentally found a way to increase productivity. The effect was an important milestone in industrial and organizational psychology, organizational behavior, and Ergonomics. However, some researchers have questioned the validity of the effect because of the experimental design and faulty interpretations. (See below: Interpretation, criticism, and conclusions).

# The Hawthorne Experiments
Like the Hawthorne effect, the definition of the Hawthorne experiments also varies.  Most industrial/occupational psychology and organizational behavior textbooks refer to the illumination studies, and usually to the relay assembly test room experiments and the bank wiring room experiments. Only occasionally are the rest of the studies mentioned..

## Relay assembly experiments
The researchers wanted to identify how other variables could affect productivity.  They chose two women as test subjects and asked them to choose four other workers to join the test group.  Together the women worked in a separate room over the course of five years (1927-1932) assembling telephone relays.
Output was measured mechanically by counting how many finished relays each dropped down a chute. This measuring began in secret two weeks before moving the women to an experiment room and continued throughout the study. In the experiment room, they had a supervisor who discussed changes with them and at times used their suggestions. Then the researchers spent five years measuring how different variables impacted the group's and individuals' productivity. Some of the variables were:
- changing the pay rules so that the group was paid for overall group production, not individual production
- giving two 5-minute breaks (after a discussion with them on the best length of time), and then changing to two 10-minute breaks (not their preference). Productivity increased, but when they received six 5-minute rests, they disliked it and reduced output.
- providing food during the breaks
- shortening the day by 30 minutes (output went up); shortening it more (output per hour went up, but overall output decreased); returning to the earlier condition (where output peaked).
Changing a variable usually increased productivity, even if the variable was just a change back to the original condition. However it is said that this is the natural process of the human being to adapt to the environment without knowing the objective of the experiment occurring. Researchers concluded that the workers worked harder because they thought that they were being monitored individually.
Researchers hypothesized that choosing one's own coworkers, working as a group, being treated as special (as evidenced by working in a separate room), and having a sympathetic supervisor were the real reasons for the productivity increase. One interpretation, mainly due to Mayo, was that "the six individuals became a team and the team gave itself wholeheartedly and spontaneously to cooperation in the experiment." (There was a second relay assembly test room study whose results were not as significant as the first experiment.)

## Bank wiring room experiments
The purpose of the next study was to find out how payment incentives would affect group productivity.  The surprising result was that they had no effect.  Ironically, this contradicted the Hawthorne effect: although the workers were receiving special attention, it didnt affect their behavior or productivity.  However, the informal group dynamics studied were a new milestone in organizational behavior.
The study was conducted by Mayo and W. Lloyd Warner between 1931 and 1932 on a group of 14 men who put together telephone switching equipment. The researchers found that although the workers were paid according to individual productivity, productivity did not go up because the men were afraid that the company would lower the base rate. Detailed observation between the men revealed the existence of informal groups or  cliques  within the formal groups. These cliques developed informal rules of behaviour as well as mechanisms to enforce them.  The cliques served to control group members and to manage bosses; when bosses asked questions, clique members gave the same responses, even if they were untrue. These results show that workers were more responsive to the social force of their peer groups than to the control and incentives of management. Hence it is of managers  interest to collaborate with these informal groups to increase cohesion for the company's benefits.

# Definitions
Here are some sample definitions of the Hawthorne effect, showing how differently it can be defined:
- An experimental effect in the direction expected but not for the reason expected; i.e., a significant positive effect that turns out to have no causal basis in the theoretical motivation for the intervention, but is apparently due to the effect on the participants of knowing themselves to be studied in connection with the outcomes measured.
- The Hawthorne Effect  the confounding that occurs if experimenters fail to realize how the consequences of subjects' performance affect what subjects do.
- People singled out for a study of any kind may improve their performance or behavior, not because of any specific condition being tested, but simply because of all the attention they receive.
- People will respond positively to any novel change in work environment

# Interpretation, criticism, and conclusions
H. McIlvaine Parsons (1974) argues that in 2a (first case) and 2d (fourth case) they had feedback on their work rates; but in 2b they didn't. He argues that in the studies 2a-d, there is at least some evidence that the following factors were potent:
- Rest periods
- Learning, given feedback i.e. skill acquisition
- Piecework pay where an individual does get more pay for more work, without counter-pressures (e.g. believing that management will just lower pay rates).
Clearly the variables the experimenters manipulated were neither the only nor the dominant causes of productivity changes. One interpretation, mainly due to Mayo, was that "the six individuals became a team and the team gave itself wholeheartedly and spontaneously to cooperation in the experiment." In 1955 Landsberger reinterpreted the experimental outcomes as the more general result of being observed and labeled this result the "Hawthorne effect."
Parsons redefines "the Hawthorne effect as the confounding that occurs if experimenters fail to realize how the consequences of subjects' performance affect what subjects do" . So he is saying it is not attention or warm regard from experimenters, but either a) actual change in rewards b) change in provision of feedback on performance. His key argument is that in 2a the "girls" had access to the counters of their work rate, which they didn't previously know at all well.
It is notable however that he refuses to analyze the illumination experiments, which don't fit his analysis, on the grounds that they haven't been properly published and so he can't get at details, whereas he had extensive personal communication with Roethlisberger and Dickson.
It's possible that the illumination experiments were explained by a longitudinal learning effect. But Mayo says it is to do with the fact that the workers felt better in the situation, because of the sympathy and interest of the observers. He does say that this experiment is about testing overall effect, not testing factors separately. He also discusses it not really as an experimenter effect but as a management effect: how management can make workers perform differently because they feel differently. A lot to do with feeling free, not feeling supervised but more in control as a group. The experimental manipulations were important in convincing the workers to feel this way: that conditions were really different. The experiment was repeated with similar effects on mica splitting workers.
References to the "the Hawthorne effect" rely on Mayo's interpretation in terms of workers' perceptions, but the data show strikingly continuous improvement. It seems quite a different interpretation might be possible: learning, expertise, reflection -- all processes independent of the experimental intervention. However, the usual Mayo interpretation is certainly a real possible issue in designing studies in education and other areas, regardless of the truth of the original Hawthorne study.
Recently the issue of "implicit social cognition", i.e., how much weight is actually given to what is implied by others' behavior towards us (as opposed to what they say, e.g. flattery) has been discussed: this must be an element here too.
Richard E. Clark and Timothy F. Sugrue (1991, p.333) in a review of educational research say that uncontrolled novelty effects (i.e. halo effect) cause on average 30% of a standard deviation (SD) rise (i.e. 50%-63% score rise), which decays to small level after 8 weeks. In more detail: 50% of a SD for up to 4 weeks; 30% of SD for 5-8 weeks; and 20% of SD for > 8 weeks, (which is < 1% of the variance).

# Can the research be trusted?
Candice Gleim says:
Broad experimental effects and their classifications can be found in Donald T. Campbell & Stanley, J. C. (1966). Experimental and quasi-experimental designs for research. Chicago: Rand McNally. and Cook, T. D., & Campbell, D. T. (1979), Quasi-Experimentation: Design and Analysis Issues. Houghton Mifflin Co.
Michael L. Kamil says:
You might want to be a bit careful about the scientific basis for the Hawthorne effect. Lee Ross has brought the concept into some question. There was a popular news story in the New York Times a couple of years ago:
David Carter-Tod says:
A psychology professor at the University of Michigan, Dr. Richard Nisbett, calls the Hawthorne effect 'a glorified anecdote.' 'Once you've got the anecdote,' he said, 'you can throw away the data.'" A dismissive comment which back-handedly tells you something about the power of anecdote and narrative.
Harry Braverman say in "Labor and Monopoly Capital":
The Hawthorne tests were based on behaviorist psychology and were supposed to confirm that workers performance could be predicted by pre-hire testing. However, the Hawthorne study showed "that the performance of workers had little relation to ability and in fact often bore a reverse relation to test scores...". What the studies really showed was that the workplace was not "a system of bureaucratic formal organization on the Weberian model, nor a system of informal group relations, as in the interpretation of Mayo and his followers but rather a system of power, of class antagonisms". This discovery was a blow to those hoping to apply the behavioral sciences to manipulate workers in the interest of management.
What may be wrong about the quoted dismissiveness is that there was not one study, but three illumination experiments, and 4 other experiments: only one of these seven is alluded to. What is right is that a) there certainly are significant criticisms of the method that can be made and b) most subsequent writing shows a predisposition to believe in the Hawthorne effect, and a failure to read the actual original studies.

# Can the literature be trusted?
The experiments were quite well enough done to establish that there were large effects due to causal factors other than the simple physical ones the experiments had originally been designed to study. The output ("dependent") variables were human work, and the educational effects can be expected to be similar (but it is not so obvious that medical effects would be). The experiments stand as a warning about simple experiments on human participants viewed as if they were only material systems. There is less certainty about the nature of the surprise factor, other than it certainly depended on the mental states of the participants: their knowledge, beliefs, etc.
Candidate causes are:
- Material factors, as originally studied e.g. illumination, ...
- Motivation or goals e.g. piecework, ...
- Feedback: can't learn skill without good feedback. Simply providing proper feedback can be a big factor. This can often be a side effect of an experiment, and good ethical practice promotes this further. Yet perhaps providing the feedback with nothing else may be a powerful factor.
- The attention of experimenters.
Parsons implies that (4) might be a "factor" as a major heading in our thinking, but as a cause can be reduced to a mixture of (2) and (3). That is: people might take on pleasing the experimenter as a goal, at least if it doesn't conflict with any other motive; but also, improving their performance by improving their skill will be dependent on getting feedback on their performance, and an experiment may give them this for the first time. So you often won't see any Hawthorne effect -- only when it turns out that with the attention came either usable feedback or a change in motivation.
Adair (1984): warns of gross factual inaccuracy in most secondary publications on Hawthorne effect. And that many studies failed to find it, but some did. He argues that it should be viewed as a variant of Orne's (1973) experimental demand characteristics. So for Adair, the issue is that an experimental effect depends on the participants' interpretation of the situation; that this may not be at all like the experimenter's interpretation and the right method is to do post-experimental interviews in depth and with care to discover participants' interpretations. So he thinks it is not awareness per se, nor special attention per se, but participants' interpretation must be investigated in order to discover if/how the experimental conditions interact with the participants' goals (in participants' views). This can affect whether participants' believe something, if they act on it or don't see it as in their interest, etc.
Rosenthal and Jacobson (1992) ch.11 also reviews and discusses the Hawthorne effect.
Its interpretation in management research
The research was and is relevant firstly in the 'Human Resources Management' movement. The discovery of the effect was most immediately a blow to those hoping to apply the behavioral sciences to manipulate workers in the interest of management.
Other interpretations it has been linked to are: Durkheim's 'anomie' concept; the Weberian model of a system of bureaucratic formal organization; a system of informal group relations, as in the interpretation of Mayo and his followers; a system of power, of class antagonisms.

# Summary view of Hawthorne
In the light of the various critiques, we can see the Hawthorne effect at several levels.
At the top level, it seems clear that in some cases there is a large effect that experimenters did not anticipate, that is due to participants' reactions to the experiment itself. It only happens sometimes. So as a methodological heuristic (that you should always think about this issue) it is useful, but as an exact predictor of effects, it is not: often there is no Hawthorne effect of any kind. To understand when and why we will see a Hawthorne or experimenter effect, we need more detailed considerations.
At a middle level Adair (1984) says that the most important (though not the only) aspect of this is how the participants interpret the situation. Interviewing them (after the "experiment" part) would be the way to investigate this.
This is important because factory workers, students, and most experimental participants are doing things at the request of the experimenter. What they do depends on what their personal goals are, how they understand the task requested, whether they want to please the experimenter and/or whether they see this task as impinging on other interests and goals they hold, what they think the experimenter really wants. Besides all those issues that determine their goals and intentions in the experiment, further aspects of how they understand the situation can be important by affecting what they believe about the effects of their actions. Thus the experimenter effect is really not one of interference, but of a possible difference in the meaning of the situation for participants and experimenter. Since all voluntary action (i.e. actions in most experiments) depends upon the actor's goals AND on their beliefs about the effects of their actions, differences in understanding of the situation can have big effects.
At the lowest level is the question of what the direct causal factors might be. These could include::
- Material ones that are intended by the experimenter
- Feedback that an experiment might make available to the participants
- Changes to goals, motivation, and beliefs about action effects induced by the experimental situation.