The statistical objective in survey research and in a number of other applications is generally to estimate the parameters of a finite population rather than to estimate the parameters of a statistical model. As an example, the finite population for a survey conducted to estimate the unemployment rate might be all adults aged 18 or older living in a country at a given date. If valid estimates of the parameters of a finite population are to be produced, the finite population needs to be defined very precisely and the sampling method needs to be carefully designed and implemented. This entry focuses on the estimation of such finite population parameters using what is known as the randomization or design-based approach. Another approach that is particularly relevant when survey data are used for analytical purposes, such as for regression analysis, is known as the superpopulation approach ( see the entry Superpopulation Models in Survey Sampling).