One of the important objectives of scientific studies is to estimate quantities of interest from a population of subjects. These quantities are called parameters, and the actual nature of the parameter varies from population to population and from study to study. For example, in a study designed to estimate the proportion of U.S. citizens who approve the President's economic stimulus plan, the parameter of interest is a proportion. In other cases, parameters may be the population mean, variance, median, and so on. In cases where the population values are represented by a parametric model, the parameters represent the whole population instead of a particular characteristic of it.

Parameters are estimated based on the sample values. Estimators are functions of sample observations used to estimate the parameter. ...