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Generally, a null result is a result which is null (nothing): that is, the proposed result is absent.* In science, it is an experimental outcome which does not show an otherwise expected effect. This does not imply a result of zero or nothing, simply a result that does not support the theory. The term is a translation of the scientific Latin nullus resultarum, roughly meaning "none as a consequence".
Statistics
In statistics, specifically, a null result occurs when there are non-significant differences between experimental and control conditions. While some differences may in fact be observed, they are below the threshold set prior to testing. The cutoff for these significance values varies, but is often .05. This is considered evidence for the null hypothesis.
Physics
In physics, the results of the Michelson-Morley experiment (MMX) were of this type, as it did not detect the expected velocity relative to the postulated luminiferous aether. This experiment's famous failed detection, commonly referred to as the null result, contributed to the development of Special relativity. Note that the MMX did in fact appear to measure a non-zero "drift", but the value was far too small to account for the theoretically expected results; it is generally thought to be inside the noise level of the experiment.
Logic
In logic, a null result is an invalid value of a proposition. It is one of the possibilities in a three-valued logic (true, false, or null result).
Law
In law, a null result is something lacking any legal or binding force.
External links
"Null result"