In statistics and machine learning, the bias–variance tradeoff is the property of a model that the variance of the parameter estimated across samples can be reduced by increasing the bias in the estimated parameters.

The Allan variance (AVAR), also known as two-sample variance, is a measure of frequency stability in clocks, oscillators and amplifiers. It is named after David W.

n. 1) an exception to a zoning ordinance, authorized by the appropriate governmental body such as a planning commission, zoning board, county commissioners or city council. Example: the zoning ordinance requires that no residences can be built within 10 feet of a property's back line, but due to the odd shape of May Matheson's property, she needs to build her dream house within five feet of the property line at one point. The local zoning board listens to her plea, finds that the neighbors do not object, and grants her a variance to build closer to the back line. 2) a difference between what the prosecution has charged and what it has proved against a criminal defendant. 3) a difference between what is alleged in a civil complaint and what is proved. A substantial variance may be fatal to the prosecution's case against the accused or fatal to a plaintiff's (the person who filed the suit) lawsuit. In each case the judge can dismiss the case as a matter of law, without sending the factual issues to the jury. In criminal cases the test of a fatal variance is somewhat stricter than in a civil lawsuit, since a minor difference between the charge and the proof may mislead the defendant and deny him/her "due process." See also: dismissal proof