In statistics, an estimator is a rule for calculating an estimate of a given quantity based on observed data: thus the rule, the quantity of interest and its result are distinguished. For example, the sample mean is a commonly used estimator of the population mean.
Comparison between good and bad estimator.
Image: Good estimator
Image: Bad estimator
Statistics is the discipline that concerns the collection, organization, analysis, interpretation, and presentation of data. In applying statistics to a scientific, industrial, or social problem, it is conventional to begin with a statistical population or a statistical model to be studied. Populations can be diverse groups of people or objects such as "all people living in a country" or "every atom composing a crystal". Statistics deals with every aspect of data, including the planning of data collection in terms of the design of surveys and experiments.
Bernoulli's Ars Conjectandi was the first work that dealt with probability theory as currently understood.
Carl Friedrich Gauss made major contributions to probabilistic methods leading to statistics.
Karl Pearson, a founder of mathematical statistics