Observer effect, observer bias, observation effect, or observation bias may refer to a number of concepts, some of them closely related:

General experimental biases

• Hawthorne effect, a form of reactivity in which subjects modify an aspect of their behavior, in response to their knowing that they are being studied
• Observer-expectancy effect, a form of reactivity in which a researcher's cognitive bias causes them to unconsciously influence the participants of an experiment
• Observer bias, a detection bias in research studies resulting for example from an observer's cognitive biases

Physics

• Observer effect (physics), the impact of observing a physical system
• Probe effect, the effect on a physical system of adding measurement devices, such as the probes of electronic test equipment

Computing

• Heisenbug of computer programming, in which a software bug seems to disappear or alter its behavior when one attempts to study it
• Observer effect (information technology), the impact of observing a process while it is running

Other uses

• "Observer Effect" (Star Trek: Enterprise), an episode of Star Trek: Enterprise, named after the effect in physics

See also

• Actor–observer asymmetry, a bias one makes when forming attributions about the behavior of others or themselves
• Demonstration effect, a effect on the behavior of an individual caused by observation of the actions of others and their consequences
• Personal equation, the idea that different observers have different reaction times, which can introduce bias when it comes to measurements and observations
• Placebo and nocebo effects, positive and negative effects autosuggested by a patient under an inert substance or treatment
• Schrödinger's cat, a thought experiment that illustrates a paradox of quantum superposition, devised by Austrian physicist Erwin Schrödinger
• Uncertainty principle, any of a variety of mathematical inequalities in quantum mechanics, introduced by German physicist Werner Heisenberg