Purity

The purity of a sample is defined as the fraction of events or objects that are of the desired type. For instance, an electron sample containing 98% genuine electrons and 2% muons has a purity of 98%. Analyses usually strive for high-purity samples. In practice, the purity that it is feasible to achieve must be balanced against the selection efficiency: in general, one wants high efficiency and purity, but it is often not possible to increase one without decreasing the other.

The opposite of purity is contamination, which can be defined as 1 – purity.