Reactivity is a phenomenon that occurs when individuals alter their performance or behavior due to the awareness that they are being observed. The change may be positive or negative, and depends on the situation. It is a significant threat to a research study's internal validity

Internal validity

Internal validity is the validity of inferences in scientific studies, usually based on experiments as experimental validity.- Details :...

 and is typically controlled for using blind experiment designs.

There are several forms of reactivity. The Hawthorne effect

Hawthorne effect

The Hawthorne effect is a form of reactivity whereby subjects improve or modify an aspect of their behavior being experimentally measured simply in response to the fact that they know they are being studied, not in response to any particular experimental manipulation.The term was coined in 1950 by...

 occurs when research study participants know they are being studied and alter their performance because of the attention they receive from the experimenters. The John Henry effect

John Henry effect

The John Henry effect is an experimental bias introduced into social experiments by reactive behavior by the control group. It is essentially the opposite of the Hawthorne Effect....

, a specific form of Hawthorne effect, occurs when the participants in the control group alter their behavior out of awareness that they are in the control group.

Reactivity is not limited to changes in behaviour in relation to being merely observed; it can also refer to situations where individuals alter their behavior to conform to the expectations of the observer.
An experimenter effect occurs when the experimenters subtly communicate their expectations to the participants, who alter their behavior to conform to these expectations. The Pygmalion effect

Pygmalion effect

The Pygmalion effect, or Rosenthal effect, refers to the phenomenon in which the greater the expectation placed upon people, often children or students and employees, the better they perform...

 occurs when students alter their behavior to meet teacher expectations. Both experimenter effects and Pygmalion effects can be caused by bias

Bias

Bias is an inclination to present or hold a partial perspective at the expense of alternatives. Bias can come in many forms.-In judgement and decision making:...

 and stereotyping, as demonstrated by studies involving stereotype threat

Stereotype threat

Stereotype threat is the experience of anxiety or concern in a situation where a person has the potential to confirm a negative stereotype about their social group. First described by social psychologist Claude Steele and his colleagues, stereotype threat has been shown to reduce the performance of...

.

See also

• Bradley effect
  Bradley effect
  The Bradley effect, less commonly called the Wilder effect, is a theory proposed to explain observed discrepancies between voter opinion polls and election outcomes in some United States government elections where a white candidate and a non-white candidate run against each other...
  
  
• Social desirability bias
  Social desirability bias
  Social desirability bias is the tendency of respondents to answer questions in a manner that will be viewed favorably by others. It can take the form of over-reporting good behavior or under-reporting bad behavior. The tendency poses a serious problem with conducting research with self-reports,...
  
  
• Observer effect
  Observer effect
  Observer effect may refer to:* Observer effect , the impact of observing a process while it is running* Observer effect , the impact of observing a physical system...
  
  
• Demand characteristics
  Demand characteristics
  In research, and particularly psychology, demand characteristics refers to an experimental artifact where participants form an interpretation of the experiment's purpose and unconsciously change their behavior accordingly. Pioneering research was conducted on demand characteristics by Martin Orne...