Beta is often used to denote a variable in mathematics and physics, where it often has specific meanings for certain applications. In physics a stream of unbound energetic electrons is commonly referred to as beta radiation or beta rays. Decays producing electrons or their antiparticles are called beta decays. In regression analysis, symbolizes nonstandardized partial slope coefficients, whereas represents standardized (standard deviation-score form) coefficients; in both cases, the coefficients reflect the change in the criterion Y per one-unit change in the value of the associated predictor X. β is also used in biology, for instance in β-Carotene, a primary source of provitamin A, or the β cells in pancreatic islets, which produce insulin.