A variety of methods are used in econometrics to estimate models consisting of a single equation. The oldest and still the most commonly used is the Ordinary Least Squares method used to estimate linear regressions. Least squares is a mathematical optimization technique that attempts to find a best fit to a set of data by attempting to minimize the sum of the squares of the differences (called residuals) between the fitted function and the data. ...

A variety of methods are available to estimate nonlinear models.

A particularly important class of non-linear models are those used to estimate relationships where the dependent variable is discrete, truncated or censored. These include logit, probit and Tobit models. In mathematics, especially as applied in statistics, the logit (pronounced with a long o and a soft g, IPA ) of a number p between 0 and 1 is Plot of logit in the range 0 to 1, base is e (The base of the logarithm function used here is of... In probability theory and statistics the probit function is the inverse cumulative distribution function, or quantile function of the normal distribution. ... The Book of Tobit is a book of scripture that is part of the Catholic and Orthodox biblical canon, pronounced canonical by the Council of Carthage of 397 and confirmed for Roman Catholics by the Council of Trent (1546). ...

Single equation methods may be applied to time-series, cross section or panel data.