Observer effect may refer to:
- Hawthorne effect, a form of reactivity in which subjects modify an aspect of their behavior, in response to the fact that they know that they are being studied.
- Heisenbug of computer programming, where 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
- Observer effect (physics), the impact of observing a physical system
- Observer-expectancy effect, a form of reactivity in which a researcher's cognitive bias causes them to unconsciously influence the participants of an experiment.
It may also refer to:
- Observer Effect, an episode of Star Trek: Enterprise, named after this effect
It is sometimes conflated with: