Observer effect

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The observer effect, or observer bias, refers to several things in different situations, though there are similarities.

1 Use in science
2 Use in Information Technology
3 Use in the social sciences
4 Observer bias
5 See also
6 References

[edit] Use in science

In science, the observer effect refers to changes that the act of observing has on the phenomenon being observed. For example: observing an electron will change its path because the observing light or radiation contains enough energy to disturb it.

In quantum mechanics, if the outcome of an event has not been observed, it exists in a state of superposition, which is being in all possible states at once. The most famous example is the thought experiment Schrödinger's cat, in which the cat is neither alive nor dead until observed — until that time, the cat is both alive and dead (technically half-alive and half-dead in probability terms).

In physics, a more mundane observer effect can be the result of instruments that by necessity alter the state of what they measure in some manner. For instance, in electronics, ammeters and voltmeters usually need to be connected to the circuit, and so by their very presence affect the current or the voltage they are measuring. Likewise, a standard mercury-in-glass thermometer must absorb some thermal energy to record a temperature, and therefore changes the temperature of the body which it is measuring.

The Heisenberg uncertainty principle is frequently, but incorrectly, confused with the "observer effect", as it relates precision in measurements related to changes in velocity and position of certain particles relative to the perspective the observer takes on them.

[edit] Use in Information Technology

In Information Technology, the observer effect refers to potential impact of the act of observing a process output while the process is running. For example: if a process uses a log file to record its progress, the act of viewing the file while the process is running could cause an I/O error in the process, which could, in turn, cause it to stop.

Another example would be observing the performance of a CPU by running the observing program on the same CPU, which will lead to inaccurate results.

Debugging a program by modifying its source code (such as adding extra output or generating log files) or by running it in a debugger may sometimes cause certain bugs to diminish or change their behavior, creating extra difficulty for the person trying to isolate the bug. (See Heisenbug)

[edit] Use in the social sciences

In the social sciences and general usage, the effect refers to how people change their behavior when it is observed and set down. People often do not behave in their usual manner when aware of being watched (see Hawthorne effect).

In the armed forces, an announced inspection is used to see how well soldiers can do when they put their minds to it, while a surprise inspection is used to see how well prepared they generally are.

In parapsychology, the observer effect refers to the situation of an experiment subject's expectations creating the experiment's results. The phrase was coined by two friends performing an experiment wherein they set up a number of volunteers who had to press the button when they felt they were being watched by the experimenters.

[edit] Observer bias

The related social-science term observer bias is error introduced into measurement when observers overemphasize behavior they expect to find and fail to notice behavior they do not expect. This is why medical trials are normally double-blind rather than single-blind. Observer bias can also be introduced because researchers see a behavior and interpret it according to what it means to them, whereas it may mean something else to the person showing the behavior. See subject-expectancy effect and observer-expectancy effect.