A word introduced by Galton that derives from his phrase ‘regression towards the mean’. It is often used as shorthand for linear regression or multiple regression models. In these models the expected value of one variable Y is presumed to be dependent on one or more other variables (x₁, x₂,…). The variable Y is variously known as the response variable, dependent variable, or outcome variable. The x-variables are variously known as antecedent variables, background variables, predictor variables, explanatory variables, controlled variables, or, potentially confusingly, independent variables. In the context of a factorial experiment (see factorial design) the x-variables are factors. See linear regression.